Immunobiology of chimeric antigen receptor T cells and novel designs.

Advances in the development of immunotherapies have offered exciting new options for the treatment of malignant diseases that are refractory to conventional cytotoxic chemotherapies. The adoptive transfer of T cells expressing chimeric antigen receptors (CARs) has demonstrated dramatic results in clinical trials and highlights the promise of novel immune-based approaches to the treatment of cancer. As experience with CAR T cells has expanded with longer follow-up and to a broader range of diseases, new obstacles have been identified which limit the potential lifelong benefits of CAR T cell therapy. These obstacles highlight not only the gaps in knowledge of the optimal clinical application of this "living drug", but also gaps in our understanding of the fundamental biology of CAR T cells themselves. In this review, we discuss the obstacles facing CAR T cell therapy, how these relate to our current understanding of CAR T cell biology and approaches to enhance the clinical efficacy of this therapy.

Murine allogeneic CD19 CAR T cells harbor potent antileukemic activity but have the potential to mediate lethal GVHD.

Acute lymphoblastic leukemia (ALL) persisting or relapsing following bone marrow transplantation (BMT) has a dismal prognosis. Success with chimeric antigen receptor (CAR) T cells offers an opportunity to treat these patients with leukemia-redirected donor-derived T cells, which may be more functional than T cells derived from patients with leukemia but have the potential to mediate graft-versus-host disease (GVHD). We, together with others, have previously demonstrated tumor-specific T-cell dysfunction in the allogeneic environment. Here, we studied CAR T-cell function following BMT using an immunocompetent murine model of minor mismatched allogeneic transplantation followed by donor-derived CD19-CAR T cells. Allogeneic donor-derived CD19-CAR T cells eliminated residual ALL with equal potency to those administered after syngeneic BMT. Surprisingly, allogeneic CAR T cells mediated lethal acute GVHD with early mortality, which is atypical for this minor mismatch model. We demonstrated that both allogeneic and syngeneic CAR T cells show initial expansion as effector T cells, with a higher peak but rapid deletion of allogeneic CAR T cells. Interestingly, CAR-mediated acute GVHD was only seen in the presence of leukemia, suggesting CAR-target interactions induced GVHD. Indeed, serum interleukin (IL)-6 was elevated only in the presence of both leukemia and CAR T cells, and IL-6 neutralization ameliorated the severity of GVHD in a delayed donor lymphocyte infusion model. Finally, allogeneic CD4(+) CAR T cells were responsible for GVHD, which correlated with their ability to produce IL-6 upon CAR stimulation. Altogether, we demonstrate that donor-derived allogeneic CAR T cells are active but have the capacity to drive GVHD.

Challenges and opportunities of allogeneic donor-derived CAR T cells.

PURPOSE OF REVIEW: As T cells engineered with chimeric antigen receptors (CARs) are entering advanced phases of clinical trial testing with promising results, the potential implications of use in an allogeneic environment are emerging as an important consideration. This review discusses the use of allogeneic CAR therapy, the potential effects of T-cell receptor (TCR) signaling on CAR T-cell efficacy, and the potential for TCR elimination to generate an off-the-shelf product. RECENT FINDINGS: The majority of preclinical and clinical data regarding allogeneic T cells are focused on safety of their use given the potential for graft-versus-host disease (GVHD) mediated by the T-cell receptor expressed with the introduced CAR. Recent clinical trials using donor-derived CAR T cells are using either rigorous patient selection or T-cell selection (such as enrichment for virus-specific T cells). Although no GVHD has been reported, the efficacy of the allogeneic CAR treatment needs to be optimized. Several preclinical models limit allogeneic CAR-driven GVHD by utilizing memory T-cell selection, virus-specific T cells, gene-editing techniques, or suicide gene engineering. SUMMARY: In the allogeneic environment, the potential effects of TCR signaling on the efficacy of CAR could affect the clinical responses with the use of donor-derived CAR T cells. Better understanding of the functionality of donor-derived T cells for therapy is essential for the development of universal effector cells for CAR therapy.

TCR engagement negatively affects CD8 but not CD4 CAR T cell expansion and leukemic clearance.

Chimeric antigen receptor (CAR)-expressing T cells induce durable remissions in patients with relapsed/refractory B cell malignancies. CARs are synthetic constructs that, when introduced into mature T cells, confer a second, non-major histocompatibility complex-restricted specificity in addition to the endogenous T cell receptor (TCR). The implications of TCR activation on CAR T cell efficacy has not been well defined. Using an immunocompetent, syngeneic murine model of CD19-targeted CAR T cell therapy for pre-B cell acute lymphoblastic leukemia in which the CAR is introduced into T cells with known TCR specificity, we demonstrate loss of CD8 CAR T cell efficacy associated with T cell exhaustion and apoptosis when TCR antigen is present. CD4 CAR T cells demonstrate equivalent cytotoxicity to CD8 CAR T cells and, in contrast, retain in vivo efficacy despite TCR stimulation. Gene expression profiles confirm increased exhaustion and apoptosis of CD8 CAR T cells upon dual receptor stimulation compared to CD4 CAR T cells and indicate inherent differences between CD4 and CD8 CAR T cells in the use of T cell-associated signaling pathways. These results provide insights into important aspects of CAR T cell immune biology and indicate opportunities to rationally design CAR constructs to optimize clinical efficacy.

CD19 CAR immune pressure induces B-precursor acute lymphoblastic leukaemia lineage switch exposing inherent leukaemic plasticity.

Adoptive immunotherapy using chimeric antigen receptor (CAR) expressing T cells targeting the CD19 B lineage receptor has demonstrated marked success in relapsed pre-B-cell acute lymphoblastic leukaemia (ALL). Persisting CAR-T cells generate sustained pressure against CD19 that may drive unique mechanisms of resistance. Pre-B ALL originates from a committed pre-B cell or an earlier progenitor, with potential to reprogram into other hematopoietic lineages. Here we report changes in lineage markers including myeloid conversion in patients following CD19 CAR therapy. Using murine ALL models we study the long-term effects of CD19 CAR-T cells and demonstrate partial or complete lineage switch as a consistent mechanism of CAR resistance depending on the underlying genetic oncogenic driver. Deletion of Pax5 or Ebf1 recapitulates lineage reprogramming occurring during CD19 CAR pressure. Our findings establish lineage switch as a mechanism of CAR resistance exposing inherent plasticity in genetic subtypes of pre-B-cell ALL.

MYC-driven accumulation of 2-hydroxyglutarate is associated with breast cancer prognosis.

Metabolic profiling of cancer cells has recently been established as a promising tool for the development of therapies and identification of cancer biomarkers. Here we characterized the metabolomic profile of human breast tumors and uncovered intrinsic metabolite signatures in these tumors using an untargeted discovery approach and validation of key metabolites. The oncometabolite 2-hydroxyglutarate (2HG) accumulated at high levels in a subset of tumors and human breast cancer cell lines. We discovered an association between increased 2HG levels and MYC pathway activation in breast cancer, and further corroborated this relationship using MYC overexpression and knockdown in human mammary epithelial and breast cancer cells. Further analyses revealed globally increased DNA methylation in 2HG-high tumors and identified a tumor subtype with high tissue 2HG and a distinct DNA methylation pattern that was associated with poor prognosis and occurred with higher frequency in African-American patients. Tumors of this subtype had a stem cell-like transcriptional signature and tended to overexpress glutaminase, suggestive of a functional relationship between glutamine and 2HG metabolism in breast cancer. Accordingly, 13C-labeled glutamine was incorporated into 2HG in cells with aberrant 2HG accumulation, whereas pharmacologic and siRNA-mediated glutaminase inhibition reduced 2HG levels. Our findings implicate 2HG as a candidate breast cancer oncometabolite associated with MYC activation and poor prognosis.

Basal-like breast cancer cells induce phenotypic and genomic changes in macrophages.

Basal-like breast cancer (BBC) is an aggressive subtype of breast cancer that has no biologically targeted therapy. The interactions of BBCs with stromal cells are important determinants of tumor biology, with inflammatory cells playing well-recognized roles in cancer progression. Despite the fact that macrophage-BBC communication is bidirectional, important questions remain about how BBCs affect adjacent immune cells. This study investigated monocyte-to-macrophage differentiation and polarization and gene expression in response to coculture with basal-like versus luminal breast cancer cells. Changes induced by coculture were compared with changes observed under classical differentiation and polarization conditions. Monocytes (THP-1 cells) exposed to BBC cells in coculture had altered gene expression with upregulation of both M1 and M2 macrophage markers. Two sets of M1 and M2 markers were selected from the PCR profiles and used for dual immunofluorescent staining of BBC versus luminal cocultured THP-1s, and cancer-adjacent, benign tissue sections from patients diagnosed with BBCs or luminal breast cancer, confirming the differential expression patterns. Relative to luminal breast cancers, BBCs also increased differentiation of monocytes to macrophages and stimulated macrophage migration. Consistent with these changes in cellular phenotype, a distinct pattern of cytokine secretion was evident in macrophage-BBC cocultures, including upregulation of NAP-2, osteoprotegerin, MIG, MCP-1, MCP-3, and interleukin (IL)-1ß. Application of IL-1 receptor antagonist (IL-1RA) to cocultures attenuated BBC-induced macrophage migration. These data contribute to an understanding of the BBC-mediated activation of the stromal immune response, implicating specific cytokines that are differentially expressed in basal-like microenvironments and suggesting plausible targets for modulating immune responses to BBCs.