Tumor-Immune Architecture and the Regulation of Antigen-Specific T-Cell Infiltration in Multiple Myeloma and Premalignant Plasma Cell Disorders

Background: Spatial aspects of immune infiltration have been extensively studied in the context of solid tumors and are correlated with response to immune therapy. Immune-based approaches have begun to transform the therapeutic landscape in hematologic malignancies such as multiple myeloma (MM) and its precursors monoclonal gammopathy of undetermined significance (MGUS) and smoldering myeloma (SMM). Bone marrow (BM) immune microenvironment in these settings has been extensively investigated with single cell analysis of BM aspirates. However, analyses of spatial patterns of tumor/immune infiltration in trephine biopsies and underlying mechanisms are poorly understood.

Methods: We combined high-dimensional spatial analyses with machine learning to analyze BM biopsies of patients with newly diagnosed MM, MGUS and SMM. Mechanisms underlying T cell infiltration into tumors were investigated with in vitro models. Growth patterns of tumor cells and mechanisms underlying infiltration of neoantigen-specific T cells were also investigated with the humanized MISTRG6 mouse model.

Results: We utilized multiplex immune fluorescence immunohistochemical analysis to evaluate trephine BM biopsies from patients with MM (n=70), MGUS (n=13) and SMM (n=12). MM but not MGUS biopsies demonstrated a multifocal pattern of tumor growth, with dense clusters of tumor cells observed in MM that appeared to create regions of T-cell exclusion in MM but not MGUS biopsies. Compared to MGUS, MM biopsies revealed a lower density of TCF1+ stem-like T cells (MGUS 190 cells/mm² versus MM 268 cells/mm², p=0.003), an increase in the proportion of granzyme B+ CD8+ effector T cells (MGUS 0.92 cells/mm2 versus MM 4.36 cells/mm², p=<0.0001), and increased expression of myeloid cells (MGUS 6.96 versus MM 9.31, p=0.0005). Multifocal growth of MM but not MGUS was reproduced in humanized MISTRG6 mice, indicating this is an intrinsic property associated with malignancy. Consistent with IHC data, MM tumors were resistant to entry of T cells in in-vitro models even when T cells are physically placed next to MM clusters. Prior activation of T cells led to increased T cell infiltration and was optimally achieved following anti-CD3/CD2/CD28 stimulation. T cell entry also required CD2/CD58 interaction and was abrogated upon disruption of these interactions. Neoantigen-specific T cells readily recognize MM cells in culture. However, entry of neoantigen-specific T cells into clusters of antigen-expressing MM tumors was antigen-specific and required in situ stimulation with antigen-presenting dendritic cells (DCs). Upon adoptive transfer into humanized mice, neoantigen-specific T cells readily localize to tumor site. However, entry of these T cells into antigen-expressing tumor masses in vivo again depends on tumor-associated DCs. Spatial analysis of IHCs from MM biopsies revealed that T cell infiltration follows a gradient from CLEC9A+ DC containing portals. Nanostring digital spatial profiling analyses indicated that CLEC9^high regions are enriched for immune activation genes, consistent with these portals as the sites of in situ immune activation and entry. Patterns of T and myeloid infiltration also correlated with both overall and progression free survival in multivariable analyses.

Conclusions: Our studies provide several novel and mechanistic insights into spatial patterns of tumor growth as well as immune infiltration in MM that impact outcomes. The concept that T cell entry depends on target recognition and costimulation provides a mechanistic basis for current redirection approaches including bispecific antibodies. These data also suggest a novel role for tumor-associated DCs in regulating entry of neoantigen-specific T cells and the effector phase of the cancer immunity cycle, with broad implications for cancer immunotherapy.

Supported in part by Specialized Center for Research Award from Leukemia and Lymphoma Society, and R35 CA197603.

Nooka:Bristol-Myers Squibb, Janssen, Takeda, Amgen, Adaptive, GlaxoSmithKline, Sanofi, Oncopeptides, Karyophram, SecureBio, and BeyondSprings: Consultancy, Honoraria. Kaufman:AbbVie, Genentech, and Bristol Myers Squibb: Consultancy; AbbVie: Other: Member of steering committee; Incyte: Other: Member of data safety monitoring committee . Hofmeister:Bristol Myers Squibb: Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen: Membership on an entity's Board of Directors or advisory committees; GlaxoSmithKline: Membership on an entity's Board of Directors or advisory committees; Sanofi: Research Funding; Genzyme: Membership on an entity's Board of Directors or advisory committees; BlueBird Bio: Honoraria. Lonial:Celgene, Janssen, Takeda: Research Funding; Novartis, BMS, GSK, Amgen, Merck, Janssen: Honoraria; AbbVie, Bluebird, Bristol-Myers Squibb, Celgene, GlaxoSmithKline, Janssen, Novartis Pharma, and Takeda.: Consultancy. Dhodapkar:Lava Therapeutics, Sanofi, Janssen: Membership on an entity's Board of Directors or advisory committees.