Functional Differences Between EBV- and CMV-Specific CD8+ T cells Demonstrate Heterogeneity of T cell Dysfunction in CLL

T-cell dysfunction in CLL is mediated through expression of Siglec-10 ligands CD24 and CD52 on CLL cells

ABSTRACT

Autologous T-cell-based therapies, such as chimeric antigen receptor (CAR) T-cell therapy, exhibit low success rates in chronic lymphocytic leukemia (CLL) and correlate with a dysfunctional T-cell phenotype observed in patients. Despite various proposed mechanisms of T-cell dysfunction in CLL, the specific CLL-derived factors responsible remain unidentified. This study aimed to investigate the mechanisms through which CLL cells suppress CAR T-cell activation and function. We found that CLL-derived T cells get activated, albeit in a delayed fashion, and specifically that restimulation of CAR T cells in the presence of CLL cells causes impaired cytokine production and reduced proliferation. Notably, coculture of T cells with CD40-activated CLL cells did not lead to T-cell dysfunction, and this required direct cell contact between the CD40-stimulated CLL cells and T cells. Inhibition of kinases involved in the CD40 signaling cascade revealed that the Spare Respiratory Capacity (SRC) kinase inhibitor dasatinib prevented rescue of T-cell function independent of CD40-mediated increased levels of costimulatory and adhesion ligands on CLL cells. Transcriptome profiling of CD40-stimulated CLL cells with or without dasatinib identified widespread differential gene expression. Selecting for surface receptor genes revealed CD40-mediated downregulation of the Sialic acid-binding Ig-like lectin 10 (Siglec-10) ligands CD24 and CD52, which was prevented by dasatinib, suggesting a role for these ligands in functional T-cell suppression in CLL. Indeed, blocking CD24 and/or CD52 markedly reduced CAR T-cell dysfunction upon coculture with resting CLL cells. These results demonstrated that T cells derived from CLL patients can be reinvigorated by manipulating CLL-T-cell interactions. Targeting CD24- and CD52-mediated CLL-T-cell interaction could be a promising therapeutic strategy to enhance T-cell function in CLL.

Chronic lymphocytic leukemia presence impairs antigen-specific CD8+ T-cell responses through epigenetic reprogramming towards short-lived effectors

T-cell dysregulation in chronic lymphocytic leukemia (CLL) associates with low response rates to autologous T cell-based therapies. How CLL affects antigen-specific T-cell responses remains largely unknown. We investigated (epi)genetic and functional consequences of antigen-specific T-cell responses in presence of CLL in vitro and in an adoptive-transfer murine model. Already at steady-state, antigen-experienced patient-derived T cells were skewed towards short-lived effector cells (SLEC) at the expense of memory-precursor effector cells (MPEC). Stimulation of these T cells in vitro showed rapid induction of effector genes and suppression of key memory transcription factors only in presence of CLL cells, indicating epigenetic regulation. This was investigated in vivo by following antigen-specific responses of naïve OT-I CD8⁺ cells to mCMV-OVA in presence/absence of TCL1 B-cell leukemia. Presence of leukemia resulted in increased SLEC formation, with disturbed inflammatory cytokine production. Chromatin and transcriptome profiling revealed strong epigenetic modifications, leading to activation of an effector and silencing of a memory profile through presence of CLL cells. Secondary challenge in vivo confirmed dysfunctional memory responses by antigen-experienced OT-I cells generated in presence of CLL. Altogether, we show that presence of CLL induces a short-lived effector phenotype and impaired memory responses by epigenetic reprogramming during primary responses.

Harnessing anti-cytomegalovirus immunity for local immunotherapy against solid tumors

Tumor infiltration by T cells profoundly affects cancer progression and responses to immunotherapy. However, the tumor immunosuppressive microenvironment can impair the induction, trafficking, and local activity of antitumor T cells. Here, we investigated whether intratumoral injection of virus-derived peptide epitopes could activate preexisting antiviral T cell responses locally and promote antitumor responses or antigen spreading. We focused on a mouse model of cytomegalovirus (CMV), a highly prevalent human infection that induces vigorous and durable T cell responses. Mice persistently infected with murine CMV (MCMV) were challenged with lung (TC-1), colon (MC-38), or melanoma (B16-F10) tumor cells. Intratumoral injection of MCMV-derived T cell epitopes triggered in situ and systemic expansion of their cognate, MCMV-specific CD4⁺ or CD8⁺ T cells. The MCMV CD8⁺ T cell epitopes injected alone provoked arrest of tumor growth and some durable remissions. Intratumoral injection of MCMV CD4⁺ T cell epitopes with polyinosinic acid:polycytidylic acid (pI:C) preferentially elicited tumor antigen-specific CD8⁺ T cells, promoted tumor clearance, and conferred long-term protection against tumor rechallenge. Notably, secondary proliferation of MCMV-specific CD8⁺ T cells correlated with better tumor control. Importantly, intratumoral injection of MCMV-derived CD8⁺ T cell-peptide epitopes alone or CD4⁺ T cell-peptide epitopes with pI:C induced potent adaptive and innate immune activation of the tumor microenvironment. Thus, CMV-derived peptide epitopes, delivered intratumorally, act as cytotoxic and immunotherapeutic agents to promote immediate tumor control and long-term antitumor immunity that could be used as a stand-alone therapy. The tumor antigen-agnostic nature of this approach makes it applicable across a broad range of solid tumors regardless of their origin.

Exploring the pathways to chronic lymphocytic leukemia

In chronic lymphocytic leukemia (CLL), increasing knowledge of the biology of the tumor cells has led to transformative improvements in our capacity to assess and treat patients. The dependence of tumor cells on surface immunoglobulin receptor signaling, survival pathways, and accessory cells within the microenvironment has led to a successful double-barreled attack with designer drugs. Studies have revealed that CLL should be classified based on the mutational status of the expressed IGHV sequences into 2 diseases, either unmutated (U) or mutated (M) CLL, each with a distinctive cellular origin, biology, epigenetics/genetics, and clinical behavior. The origin of U-CLL lies among the natural antibody repertoire, and dominance of IGHV1-69 reveals a superantigenic driver. In both U-CLL and M-CLL, a calibrated stimulation of tumor cells by self-antigens apparently generates a dynamic reiterative cycle as cells, protected from apoptosis, transit between blood and tissue sites. But there are differences in outcome, with the balance between proliferation and anergy favoring anergy in M-CLL. Responses are modulated by an array of microenvironmental interactions. Availability of T-cell help is a likely determinant of cell fate, the dependency on which varies between U-CLL and M-CLL, reflecting the different cells of origin, and affecting clinical behavior. Despite such advances, cell-escape strategies, Richter transformation, and immunosuppression remain as challenges, which only may be met by continued research into the biology of CLL.