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The Pacific Mesothelioma Center Showcases It’s Mesothelioma Research at Holiday Open House

The nonprofit medical research institute is hosting its annual holiday open house on December 6th at its in-house research lab in Los Angeles

LOS ANGELES, CA, USA, November 30, 2017 /EINPresswire.com/ — Fresh off the heels of its successful 5K Walk for Mesothelioma, The Pacific Mesothelioma Center at the Pacific Heart, Lung & Blood Institute (PHLBI) is excited to celebrate the holidays at the annual PMC Holiday Open House on Wednesday, December 6th, 2017 from 12 p.m. to 7 p.m. at the PMC office in Los Angeles. The annual open house showcases the innovative research conducted at PMC at their in-house research laboratory. Attendees will be able to meet the PMC researchers, learn about the exciting research taking place in the lab, eat delicious food from French- Moroccan eatery Chez Marie, and watch student interns perform live demonstrations.

The Pacific Heart, Lung & Blood Institute (PHLBI) is a 501(c)(3) nonprofit medical research institute that is trying to find better treatment options for diseases of the heart, lung, and blood including mesothelioma- a devastatingly under-researched and underfunded cancer that is caused by exposure to asbestos. The PHLBI operates two laboratories, one at its office on Santa Monica Blvd and the other, The Punch Worthington lab. at UCLA. The PHLBI’s current focus is on engineering mesenchymal stem cells to be used in combination with immunotherapy to treat a variety of cancers including mesothelioma.

The open house is being held at the Pacific Heart, Lung & Blood Institute’s office in Los Angeles (10780 Santa Monica Blvd, Suite 101, Los Angeles, CA, 90025) and will start at 12 p.m. and end at 7 p.m. Individuals new to the PHLBI are encouraged to attend so they can learn more about the institute, it’s exciting research, meet the researchers, and learn about the events held throughout the year to raise awareness and funds for research, including the 5K Annual Walk/Hike and The Greatest Escape Motorcycle Ride.

For more information about the Holiday Open House, please contact Clare Cameron at (310)-478-4678, or email to info@phlbi.org.

Immune Checkpoint Blockade and Adaptive Immune Resistance in Cancer

Raymond M. Wong1 and Robert B. Cameron2
Appearing in Immunology and Microbiology » “Immunotherapy – Myths, Reality, Ideas, Future”,  Published: April 26, 2017 under CC BY 3.0 license. © The Author(s).

Abstract

The clinical success of immune checkpoint blockers is a pivotal advancement for treating an increasing number of cancer types. However, immune checkpoint blockers still rarely induce complete remission and show little to no therapeutic efficacy in a significant percentage of cancer patients. Efforts are now underway to identify biomarkers that accurately predict which patients benefit from immune checkpoint blockers. Moreover, adaptive immune resistance can develop in tumors during treatment with immune checkpoint blockers. These adaptive resistance mechanisms in tumors might be disrupted by combining adjunctive immunotherapies, which could potentially improve the therapeutic efficacy of immune checkpoint blockers. This chapter discusses the mechanism of action of cytotoxic T lymphocyte antigen-4 (CTLA-4) and programmed death-1/programmed death-ligand 1 (PD-1/PD-L1) immune checkpoint blockers and biomarkers that might predict clinical responses to these drugs. Lastly, ongoing research on mechanisms of tumor adaptive resistance could facilitate rationale design of adjunctive immunotherapies that can be synergistically combined with immune checkpoint blockers to more effectively treat cancer.

Keywords: immunotherapy, T lymphocytes, immune checkpoints, CTLA-4, PD-1, PD-L1

1. Introduction

Immune checkpoints are inhibitory pathways that are critical for maintaining self-tolerance. Immune checkpoints also control the magnitude and duration of physiological immune responses in peripheral tissues in order to minimize collateral damage. Immune checkpoint receptors and their cognate ligands are naturally expressed on a variety of cell types, including antigen-presenting cells, T cells, B cells, tumor cells, tumor stroma, and also normal tissue. A number of immune checkpoint pathways have been identified, including cytotoxic T lymphocyte antigen-4 (CTLA-4), programmed death-1 (PD-1), programmed death ligand-1 (PD-L1), T cell immunoglobulin and mucin domain 1 (TIM-1), T cell immunoglobulin and mucin domain 3 (TIM-3), lymphocyte-activation gene 3 (LAG-3), T cell immunoreceptor with Ig and ITIM domains (TIGIT), V-domain Ig suppressor of T cell activation (VISTA), carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1), leukocyte-associated immunoglobulin-like receptor 1 (LAIR-1), herpesvirus entry mediator (HVEM), B- and T-lymphocyte attenuator (BTLA), CD160, CD200, CD200 receptor, and adenosine 2A receptor (A2Ar). For brevity, this chapter will focus on CTLA-4 and PD-1/PD-L1, as clinical drugs targeting these pathways have been successfully developed to treat an increasing variety of human cancer types.

2. Main body

2.1. CTLA-4

CTLA-4 is the first immune checkpoint receptor to be clinically targeted. CTLA-4 is expressed mainly on the surface of activated T cells. While certain subsets of T regulatory cells constitutively express CTLA-4, it is virtually undetectable on naïve, inactivated T cells. Upon activation, both CD4+ and CD8+ T cells upregulate CTLA-4 on the surface, reaching maximum level within 2–3 days. CD4+ T cells are reported to express more CTLA-4 mRNA and protein compared to CD8+ T cells, suggesting that CTLA-4 has a more significant regulatory effect on CD4+ T cells [1].

CTLA-4 downregulates T cell activation by sequestering CD80 and CD86 costimulatory molecules on antigen-presenting cells. This prevents CD80 and CD86 from delivering costimulatory activation signals to T cells through the CD28 receptor. CTLA-4 binds to CD80 and CD86 with ~10 times higher affinity than CD28 [2]. CTLA-4 expressed on T cells can also remove CD80 and CD86 molecules from neighboring antigen-presenting cells through a process called trans-endocytosis [3]. CTLA-4 also prevents CD28 recruitment to the immunological synapse, further impairing T cell activation [4].

CTLA-4 knockout mice die within 2–3 weeks of age due to massive lymphoproliferation, resulting in destruction of vital organs [5]. This lethal phenotype is associated primarily with hyperactivated CD4+T cells, which are skewed toward a T helper type-2 phenotype and have increased resistance to apoptosis. These hyperactivated CD4+ T cells abnormally infiltrate into peripheral tissues, resulting in organ failure. These observations led cancer immunology researchers to hypothesize that blockade of CTLA-4 signaling could potentially induce effective T cell-mediated immune responses against tumor tissue.

A pivotal laboratory study reported in 1996 by James Allison’s group showed that treatment of tumor-bearing mice with a CTLA-4-blocking antibody could effectively induce tumor regression [6]. Despite much subsequent investigation, the in vivo mechanism of action of CTLA-4 blockade immunotherapy has remained elusive. The prevailing hypothesis is that CTLA-4 blockade not only enhances T cell infiltration into tumors but also reduces the relative presence of immunosuppressive T regulatory cells in tumor tissue [7]. This alteration in the ratio of effector T cells versus T regulatory cells in tumors tilts the immunological balance in favor of T cell-mediated destruction of tumor cells.

These studies led to pharmaceutical development of the first immune checkpoint blocker, ipilimumab (Yervoy®). Ipilimumab is a fully human monoclonal antibody that blocks the CTLA-4 receptor, thereby preventing its ability to sequester CD80 and CD86 costimulatory molecules. It was initially tested in melanoma, and demonstrated extended overall survival in patients versus a comparator melanoma peptide-based immunotherapy vaccine called gp100. In a randomized phase III clinical trial, melanoma patients receiving ipilimumab had a median overall survival of 10.4 months versus 6.4 months in those receiving only the gp100 peptide vaccine (Hodi 2010). Objective response rates (measureable tumor regression) were 10.9% in the ipilimumab group versus 1.5% in the gp100 vaccine group. The responses to ipilimumab were durable, with the 1-year and 2-year survival rate being 46 and 24%, respectively. By comparison, the 1-year and 2-year survival rate in patients receiving only the gp100 peptide vaccine was only 25 and 14%, respectively [8]. These trial results led to US FDA approval of ipilimumab for melanoma in 2011.

2.2. PD-1

PD-1 is another major immune checkpoint receptor that regulates T cell activity against tumor tissue. PD-1 is a cell surface receptor originally identified in a murine T cell hybridoma undergoing programmed cell death [9]. PD-1 is absent on naïve inactivated immune cells but is significantly upregulated on activated T cells, B cells, natural killer cells and myeloid-derived cells [10]. In T cells, PD-1 expression is induced by T cell receptor signaling [11] and also by certain pro-inflammatory cytokines including interleukin-2, interleukin-7, interleukin-15, and interleukin-21 [12].

PD-1 signaling downregulates T cell activity primarily via interaction with its two natural ligands: Programmed Death Ligand-1 (PD-L1) and Programmed Death Ligand-2 (PD-L2). PD-L1 is expressed on a wide variety of cell types including hematopoietic cells, T cells, B cells, myeloid cells, and dendritic cells [10]. It is also expressed on a wide variety of peripheral tissues such as skeletal muscle, lung, heart, and placenta [10]. Notably, PD-L1 is also expressed on a wide variety of cancer cells and generally is associated with poorer patient prognosis [13]. PD-L2 expression is generally more restricted, being found primarily on dendritic cells, macrophages, and occasionally cancer cells [14]. PD-L2 binds to PD-1 with two- to sixfold higher relative affinity than PD-L1 [15]. However, PD-L2 is generally expressed at lower relative levels [16]. Thus, it is believed that PD-L1 is the predominant ligand for PD-1.

Signaling through the PD-1 receptor on T cells results in downstream inhibition of PI3K/AKT activation [17]. The net effect is downregulation of a number of effector functions including cytokine secretion and cytolytic activity. PD-1 knockout mice have various autoimmune pathologies, including autoantibody-induced cardiomyopathy [18], arthritis and lupus-like disease [19], and diabetes [20]. In peripheral tissues, the immunosuppressive activity of PD-1 is mediated primarily by interaction with PD-L1 [21]. PD-L1 expressed in tumor tissue also impairs host antitumor immune responses [22]. PD-L1 and/or PD-L2 in tumor tissue facilitates evasion from host immune responses via multiple mechanisms including induction of T cell anergy and exhaustion [23], promoting T cell apoptosis [24], and also by enhancing the expansion and activity of immunosuppressive T regulatory cells [25]. Moreover, PD-1 can transmit an antiapoptotic signal to PD-L1-expressing tumor cells, which renders them resistant to lysis by cytotoxic T lymphocytes [26].

This fundamental understanding of the PD-1/PD-L1 axis in suppressing host antitumor immune responses led to development of the first clinical PD-1 blockers, nivolumab (Opdivo®) and pembrolizumab (Keytruda®). Both nivolumab and pembrolizumab are fully human monoclonal antibodies that block the PD-1 receptor, thereby preventing its ability to bind its natural ligands PD-L1 and PD-L2. In large phase I clinical trials, nivolumab and pembrolizumab each demonstrated durable clinical response rates with acceptable safety profiles in patients with advanced melanoma, non-small cell lung cancer, renal cell carcinoma or Hodgkin’s lymphoma [2730]. Nivolumab and pembrolizumab are now both FDA approved for treating melanoma and non-small cell lung cancer. Nivolumab is additionally approved for treating renal cell carcinoma, Hodgkin’s lymphoma, and also for use in combination with the CTLA-4 blocker, ipilimumab, for treating melanoma. Remarkably, in two separate melanoma clinical trials, the combination of nivolumab and ipilimumab induced objective responses in ~60% of patients, with complete responses seen in ~11.5–22% of patients [3132].

Pembrolizumab and nivolumab (and a third investigational PD-1 blocker, pidilizumab) are now collectively continuing in 500+ clinical trials. Virtually all cancer types are now being targeted with PD-1/PD-L1 blockers in some capacity. Notably, there is a significant effort to test nivolumab or pembrolizumab with other adjunctive therapies to determine synergistic combinatorial regimens. Conventional treatments like chemotherapy and radiation have shown in animal tumor models to potentially synergize with PD-1/PD-L1 blockers [3335]. In addition, PD-1 blockers are now also being tested in combination with small molecule drugs (investigational and Food and Drug Administration (FDA) approved) and also experimental immunotherapies such as vaccines and chimeric antigen receptor T cells.

All clinical PD-1 blockers have the same mechanism of action. Slight variances in the protein structure among different PD-1 blockers could potentially confer differences in binding affinity for the PD-1 receptor and also differences in half-life (i.e. persistence in the body). The physiological significance and clinical effectiveness of such variances remain undetermined.

2.3. PD-L1

Expression of PD-L1 is found on diverse cell types, including normal and malignant tissue, antigen presenting cells, myeloid cells, B cells, and T cells. PD-L1 downregulates T cells via multiple mechanisms. PD-L1 expressed on various cells primarily interacts with PD-1 expressed on T cells, delivering an inhibitory signal that downregulates T cell activity. PD-L1 also binds to CD80 expressed on both antigen-presenting cells and activated T cells [36]. Interaction of PD-L1 with CD80 on antigen-presenting cells prevents CD80 from delivering costimulatory activating signals to T cells. When PD-L1 binds to CD80 expressed on activated T cells, an inhibitory signal is delivered to T cells. Currently, it is unknown exactly what intracellular signaling pathways are altered when PD-L1 binds to CD80 on T cells. Nonetheless, it is now generally understood that blocking PD-L1 results in enhanced T cell activation.

Atezolizumab (Tecentriq®) was the first PD-L1 blocker to enter clinical trials. Atezolizumab is a fully human monoclonal antibody that prevents PD-L1 from binding to PD-1 and CD80. It was initially tested in patients with PD-L1-positive metastatic bladder cancer [37]. Bladder cancer patients with PD-L1-negative tumors were subsequently included for treatment. Clinical response rates were ~15% of PD-L1-negative patients and ~25% of PD-L1-positive patients [37]. Because of the higher clinical activity of atezolizumab in PD-L1-positive bladder cancer, a companion diagnostic called the Ventana PD-L1 (SP142) assay is offered to provide tumor PD-L1 expression status of patients considering atezolizumab treatment. In 2016, atezolizumab was FDA approved for urothelial carcinoma, the most common form of bladder cancer. Like nivolumab and pembrolizumab PD-1 blockers, atezolizumab is now continuing in clinical trials for a wide variety cancer types and also being tested in combination with conventional cancer treatments, small molecule drugs and other investigational immunotherapies. Alternative PD-L1 blockers, such as avelumab and durvalumab, are also now in clinical trials.

2.4. PREDICTIVE BIOMARKERS FOR CTLA-4 AND PD-1/PD-L1 BLOCKERS

CTLA-4 and PD-1/PD-L1 immune checkpoint blockers have proven to be pivotal advancements in cancer treatment. However, a significant proportion of cancer patients still experience little to no clinical benefit from treatment. Even among responding patients, only a small minority achieve complete remission. Studies using clinical tumor specimens from patients treated with immune checkpoint blockers have revealed some potentially important differences between responders versus nonresponders.

During early clinical development of PD-1 blockers, it was hypothesized that differential expression levels of PD-L1 in tumor tissue would correlate with clinical responses. It was anticipated that PD-L1 expression in tumor tissue could therefore be a predictive biomarker to accurately identify patients likely to respond to PD-1 or PD-L1 blockers. However, a definitive correlation has thus far not been established. Both PD-L1-positive and PD-L1-negative tumors can respond to PD-1 or PD-L1 blockers. Further confounding factors include variability of PD-L1 expression in different anatomical areas of tumor tissue. In addition, PD-L1 expression in tumor tissue may be transient—appearing and disappearing due to treatments or other poorly understood influences. Lastly, assays measuring PD-L1 in tumors have yet to establish a clear threshold of expression that defines what is considered “PD-L1-positive.” For instance, the FDA-approved Ventana PD-L1 assay defines ≥5% PD-L1-positive cells in bladder cancer tissue to be associated with higher clinical response rates to atezolizumab [38]. However, alternative PD-L1 assays used in various other clinical trials of nivolumab or pembrolizumab have wide variability in PD-L1 expression analysis methodologies. Overall, it is generally agreed upon that low or absent PD-L1 expression in tumors is not sufficient to preclude a patient from treatment with PD-1/PD-L1 blockers [39].

Alternative predictive biomarkers for clinical response to PD-1/PD-L1 blockers are currently being explored. CD8+ T cell infiltration into tumors might be predictive of clinical response to PD-1 blockers. Specifically, the density of pretreatment CD8+ T cells at both the tumor invasive margin and tumor center may be correlated with clinical response to pembrolizumab. In serially biopsied tumors from melanoma patients undergoing pembrolizumab treatment, it was shown that responding patients generally had higher densities of CD8+/PD-1+ cells in close proximity to PD-L1-expressing tumor cells [40]. Furthermore, serial analysis of tumor biopsies showed that intratumoral CD8+/PD-1+ T cells actively proliferate during pembrolizumab treatment [40]. These data offer insights on a potential mechanism of PD-1 blockade efficacy, whereby presence of pretreatment CD8+ T cells in tumors is a prerequisite for clinical response. However, like tumor PD-L1 expression assays, establishing a standard cut-off threshold value for CD8+ T cell levels in tumors that accurately predicts clinical response to PD-1/PD-L1 blockade will be challenging. Tumors of various tissue origins often contain infiltrating T cells that can vary greatly in absolute number, density, and also anatomical location within the intratumoral space. Nonetheless, establishing a “scoring system” based on pretreatment CD8+ T cell infiltration warrants further investigation as a potential predictive biomarker.

Another intriguing biomarker with predictive potential may be intratumoral expression of indoleamine-2,3-dioxygenase (IDO). IDO is a tryptophan catabolizing enzyme that is occasionally expressed in various tumor types. Depletion of tryptophan within tumors by IDO may be a rate-limiting step for effective antitumor T cell activity. Studies in melanoma patients treated with ipilimumab suggest a correlation between pretreatment IDO expression and clinical response. In one study, intratumoral IDO was detected in 37.5% of responding melanoma patients and only 11.1% in nonresponders [41]. It remains to be seen if similar patterns are seen in other cancer types and also patients treated with PD-1/PD-L1 blockers.

Genetic signatures of tumors are yet another parameter with potential for yielding predictive biomarkers for clinical response to immune checkpoint blockers. Certain tumors, such as colorectal cancer, are highly refractory to treatment with PD-1 blockers. In early clinical trials of nivolumab, it was found that only 1 in 33 colorectal cancer patients responded to treatment [2728]. Subsequently, it was hypothesized that the single responding colorectal cancer patient harbored a defect in DNA mismatch repair in tumor tissue, resulting in a significantly high load of somatic mutations [42]. Defects in tumor tissue mismatch repair can result in thousands of somatic mutations, providing a larger pool of neo-antigens for immune recognition. Immune checkpoint blockade therapy could therefore amplify the natural adaptive immune response to mutated neo-antigens. Hence, mutational load in pretreatment tumor tissue might be predictive of clinical response to immune checkpoint blockers. To test this hypothesis, a small clinical trial focusing primarily on colorectal cancer showed that patients with defects in tumor tissue mismatch repair harbored significantly higher loads of somatic mutations versus those with mismatch repair-proficient tumors. Upon treatment with pembrolizumab, higher response rates and longer survival times were seen in patients with mismatch repair defects versus those with proficient mismatch repair [42]. This pivotal study has catalyzed further investigation of tumor mutational profiles to determine if a correlation with clinical responses can be established in large studies of diverse cancer types.

2.5. ADAPTIVE IMMUNE RESISTANCE

Mechanisms of inherent and acquired resistance to immune checkpoint blockade are poorly understood. Clinical responses to CTLA-4 and PD-1/PD-L1 blockers are often durable, sometimes lasting years. However, complete regressions are still relatively rare and eventual disease relapse among responding patients is frequent. Recent studies have offered insights that immunological parameters of tumor tissue adapt in response to T cell-mediated attack induced by immune checkpoint blockers. Enhanced T cell activity within tumors involves local production of inflammatory mediators, such as interferon (IFN)-γ, which is known to upregulate PD-L1 on peripheral tissues [43]. Upregulation of PD-L1 on various cell types within tumor tissue might result in heightened CD80-mediated inhibition of proximal effector T cells.

Furthermore, augmentation of effector T cell activity in tumor tissue via PD-1 blockade may subsequently induce compensatory upregulation of alternative immune checkpoint receptors, TIM-3. TIM-3 is a receptor expressed primarily on IFN-γ-secreting CD4+ and CD8+ T cells [44]. TIM-3 is bound by multiple ligands, including galectin-9, CEACAM-1, and high-mobility group box 1 (HMGB-1). Signaling through TIM-3 in activated T cells triggers the release of human leukocyte antigen B-associated transcript 3 (BAT3) from the TIM-3 cytoplasmic domain. This results in defective production of IL-2, IFN-γ, and likely other pro-inflammatory cytokines [44]. Although the TIM-3 signaling pathway has yet to be fully elucidated, it seems clear that TIM-3 affects T cell receptor downstream signaling via a mechanism distinct from PD-1 and CTLA-4.

TIM-3 appears to be co-expressed with PD-1 in tumor-infiltrating lymphocytes of cancer patients and is upregulated on T cells upon therapeutic PD-1 blockade [45]. This may provide a mechanism of immunological escape and a possible reason for incomplete clinical responses upon PD-1 blockade immunotherapy. It might also be a contributing factor toward acquired resistance to PD-1 blockade clinically, whereby patients initially respond to treatment but eventually relapse despite continuous therapy. Preclinical studies in animal tumor models show that PD-1 blockade immunotherapy results in upregulation of TIM-3 on T cells. Co-blockade of both TIM3 and PD-1 can prevent resistance to PD-1 blockade immunotherapy [45]. As such, TIM-3 blocking antibodies are now in early phase clinical trials to evaluate their safety, tolerability, and dosing ranges. Figure 1 illustrates how PD-1/PD-L1 blockade may result in compensatory upregulation of TIM-3 and/or PD-L1 on T cells and tumor cells.

media/F1.png

FIGURE  1.

PD-1/PD-L1 blockade promotes T cell-mediated inflammation in tumors. In turn, this can trigger upregulation of PD-L1 on various cells within tumor tissue. This can also trigger compensatory upregulation of TIM-3 on effector T cells. Upregulation of PD-L1 and TIM-3, even during continuous treatment with PD-1 blockers, can impair T cell activity and result in clinical resistance.

Downregulation of major histocompatibility (MHC) receptor expression in tumors might also contribute to acquired resistance to PD-1 blockers. Loss-of-function mutations in the MHC beta-2 microglobulin antigen-presenting protein have been noted in selected melanoma patients who initially responded to pembrolizumab therapy but subsequently relapsed [46]. Further studies in larger patient populations are necessary to confirm the association of MHC-related mutations and acquired resistance to PD-1 blockers.

2.6. STRATEGIES TO COUNTERACT ADAPTIVE RESISTANCE TO IMMUNE CHECKPOINT BLOCKADE

The mechanism of inherent and acquired/adaptive resistance to CTLA-4 and PD-1/PD-L1 immune checkpoint blockers is not fully understood and could possibly vary between individual patients and different tumor types. However, research on predictive biomarkers and mechanisms of adaptive resistance to PD-1 blockers have yielded insight that might be extrapolated to rationally design combination immunotherapies that synergistically enhance the efficacy of immune checkpoint blockers. For instance, it is now generally understood that PD-1 blockers augment T cell-mediated inflammation in tumor tissue. In turn, this can promote upregulation of PD-L1 on various cells in tumors, likely due to IFN-γ signaling [43]. Upregulation of PD-L1 expression in tumor tissue can promote enhanced CD80 signaling in T cells, which impairs T cell activity [36]. PD-1 blockade may also induce compensatory upregulation of alternative immune checkpoint receptors, such as TIM-3, on T cells within tumor tissue [45]. TIM-3 signaling results in downregulation of T cell activity. Next-generation immunotherapeutic regimens might combine PD-1 blockers such as nivolumab/pembrolizumab with PD-L1 blockers like atezolizumab, to counteract PD-L1 upregulation induced by T cell-mediated inflammation in tumor tissue. Other rational combinations might include PD-1/PD-L1 blockers combined with investigational TIM-3 blockers, to counteract the effects of TIM-3 upregulation on activated T cells.

Another strategy to enhance the efficacy of immune checkpoint blockers might involve improving T cell trafficking to tumor tissue. The extent of T cell infiltration into tumor tissue may be a predictive biomarker and a prerequisite for efficacy of both CTLA-4 and PD-1/PD-L1 blockers. As such, therapies that promote T cell trafficking to tumors could potentially improve tumor sensitivity to immune checkpoint blockers. Studies of human melanoma tumors have identified a set of chemokines that are associated with enhanced recruitment of T cells toward tumor tissue. These chemokines, including CCL2, CCL3, CCL4, CCL5, CXCL9, and CXCL10, might have utility as clinical therapies to improve T cell trafficking to tumors [47]. However, such chemokines or other T cell recruitment factors must be targeted specifically to tumor tissue in order to effectively recruit T cells. T cell recruitment factors might be coupled to antibodies that bind to tumor cell receptors, thus providing a vehicle for tumor targeting. In animal tumor studies, a T cell recruitment factor called LIGHT (also called tumor necrosis factor superfamily member 14) was fused to an anti-epidermal growth factor receptor (EGFR) antibody. This LIGHT-anti-EGFR fusion molecule was able to promote more extensive T cell infiltration into EGFR-expressing tumors. In turn, this prevented resistance to PD-L1 blockade immunotherapy [48]. Similar strategies that target other T cell recruitment factors toward tumors might be feasible.

Our group at the Pacific Heart, Lung & Blood Institute (Los Angeles, CA) is conducting research on gene-modified human mesenchymal stem cells (MSCs) as a strategy to alter the tumor microenvironment and prevent resistance to immune checkpoint blockers. MSCs can be isolated and expanded from various adult tissues including bone marrow, fat, umbilical cord blood, and term placentas. MSCs are known to preferentially migrate to tumor tissue, making them potentially useful drug delivery vectors to alter the immunological microenvironment of tumors [49]. In animal tumor models, MSCs have been genetically modified in diverse ways to effectively treat tumors. These include modification to produce immunostimulatory cytokines (e.g. IFN-α, IFN-β, IL-12) and T cell trafficking molecules such as LIGHT [5053].

Both autologous and allogeneic MSCs have been used extensively in clinical trials for treating severe inflammatory disorders and certain degenerative conditions, and generally have an acceptable safety profile [54]. Autologous gene-modified MSCs have recently entered clinical trials for cancer [55]. It remains to be seen if MSCs and other tumor-targeting systems can effectively deliver pro-inflammatory agents to tumor tissue and improve sensitivity to clinical immune checkpoint blockers.

3. Acknowledgements

Research funding at the Pacific Heart, Lung & Blood Institute is provided in part by grants from the Richard M. Schulze Family Foundation, the H.N. & Frances C. Berger Foundation, and the Kazan McClain Partners’ Foundation.

Inquires with the Investigator : Using MSC’s in Placenta’s for Mesothelioma Research

placenta

What is a placenta?

A placenta is a flattened circular organ that develops in a woman’s uterus during pregnancy. The placenta attaches to the uterine wall and develops an umbilical cord which is then used to provide oxygen and nutrients to the growing baby while simultaneously removing waste products from the baby’s blood. The day of delivery the expectant mother delivers her baby and her placenta. Placentas are usually thrown out by hospitals after delivery, some mothers elect to keep it and have it made into a pill or shake and eat it, while others decide to donate the placenta for research.

 

Placenta Donations to The Pacific Mesothelioma Center

Over the last two years The Pacific Mesothelioma Center has received six placenta donations from families. The placentas biological makeup is rich in mesenchymal stem cells which are ideal for advancing the PMC’s research agenda. This past week Lead Research Investigator Raymond Wong received another placenta donation and took the time to share his process harvesting placentas and explaining their intrinsic value to research.

 

What are you getting out of the placenta and how does it help our research?

Placenta contains mesenchymal stem cells (MSCs), a type of cell that normally serves as a reservoir to replenish tissue – primarily fat, cartilage, and bone.  MSCs can be isolated from placenta and expanded to large numbers for laboratory research and also for medical treatment.  MSCs are of interest to medical researchers as they might be useful for treating certain degenerative conditions such as arthritis, diabetes, heart maladies, and even nervous system injuries.  Due to their natural anti-inflammatory properties, MSCs might also be useful for treating inflammatory conditions such as graft-vs-host disease and Crohn’s disease.  For cancer, MSCs are believed to preferentially migrate to malignant tumors.  This opens the possibility that MSCs can be engineered to deliver anti-cancer drugs preferentially to tumors, thereby increasing the potency of anti-cancer drugs while also limiting toxic side effects.  PHLBI is working on engineering MSCs to deliver immune-boosting proteins as a form of immunotherapy.

 

Explain the significance, if any, of the sex or ethnicity of the baby’s whose placenta is donated?

MSCs harvested and grown from placentas can originate from the mother, the baby, or a mixture of both.  The composition of each batch of MSCs is unpredictable with regard to the exact mixture.  The ethnicity of the mother or baby is unlikely to have significance.  The sex of the baby may influence the level of anti-inflammatory properties of the resulting batch of harvested MSCs.  This might impact the ability of a particular MSC batch to be universally compatible with genetically diverse recipients who are infused with donated MSCs.For reference, the immune system of males vs. females is generally known to be different.  For reference, females have higher incidences of inflammatory disorders, which might suggest that MSCs from a female baby have lower anti-inflammatory properties.  The lower anti-inflammatory properties of female-derived MSCs could possibly make them more prone to being rejected when infused into a genetically unrelated recipient.

newPNG *Pictured above is Lead Investigator Raymond Wong  working on a placenta donation last week in the lab.

 

Describe the process for getting mesenchymal stem cells out of a placenta? How long does it take?      

 Placentas are first cut into small pieces, and then digested for ~2 hours with an enzyme called collagenase to loosen MSCs.  The resulting mixture of digested placental cells contains a very small percentage of MSCs.  By growing the digested placental cell mixture in specialized nutrients, the small number of MSCs is expanded exponentially to large numbers.  This process results in nearly 100% purified MSCs within 3-4 weeks.

 

What is the difference between a placenta from a c-section and placenta from natural birth?

Biologically, there is no difference.  The main impact of c-section vs. natural birth is the amount of microbial contaminants on the placenta when it is obtained.  C-section is a sterile surgery, resulting in lower microbial contaminants.  Natural birth passes the placenta through the virginal canal, resulting in a much larger amount of microbial contaminates (yeast, bacteria, fungus, etc).  Nonetheless, our laboratory protocol for harvesting MSCs utilizes anti-fungal and antibiotic drugs to eliminate microbial contaminants.

 

 How many placenta donations are we looking to have donated each year?                                                              

We have averaged around 2-3 placenta donations each year.

 

 Are any embryonic stem cells cultivated from the placenta?                                                                                                  

MSCs are not embryonic stem cells.  They are considered “adult” stem cells, meaning they are derived from organs that have already developed (bone marrow, placenta, etc).

For questions, additional information, or inquires about how one can donate their placenta to research contact Lead Investigator Raymond Wong at (310)-474-1113 or by email at : rwong@phlbi.org .