Restoring Innate and Adaptive Immune Repertoire in Multiple Myeloma for Therapeutic Application

Despite advances and improvements in survival, majority of multiple myeloma (MM) patients ultimately relapses. Extensive analysis on the properties of tumor cells has provided interesting insights into the disease biology allowing for the identification of novel targets and development of related therapeutics. However, the key microenvironmental influences, especially immune microenvironment, that drive the disease and impact outcome remain to be fully characterized.

We have now performed both single cell RNA-sequencing and high-dimensional CyTOF analysis of both peripheral blood (PBMC) and bone marrow mononuclear cells (BMMC) from MM patients and healthy donors (HD) and evaluated both phenotypic and functional state of the MM immune repertoire. In addition to humoral immunodeficiency impacting aberrations in B-cell subsets (B1a, B1b, B2 and Breg cells) and the disfunction in the adaptive immune system including an increase in the immunosuppressive cells (Tregs or myeloid-derived suppressor cells), a significant impairment of the innate immunity was identified in MM patients with a progressive decline in functional state of natural killer (NK) cells. Additionally, a lower expression of the activating receptors NKG2D and NKp46 as opposed to a higher expression of certain inhibitory KIR receptors was observed in NK cells from MM patients compared to HD. This immunosuppressive microenvironment allows tumor immune escape and ultimately myeloma cell growth.

To overcome some of the immune dysfunction observed in MM, we have evaluated the role of IL15, a key player in both innate and adaptive immunity, with antitumor activity via enhancing both NK and memory T cell functions. Using extensive flow cytometry-based analysis, we evaluated impact of recombinant IL15 on PBMC from HD and MM patients at different stages of disease. Treatment with recombinant IL15 rescued the immune effector cell decline observed in MM patients. Specifically, a 2.9-fold-increase in CD8+ CD45RO+ CCR7- effector memory T cells and a 1.5-fold-increase in NK populations in both HD and MM PBMC was observed. For a subset of MM patients, we have also confirmed these positive effects on BMMC. Importantly, cytotoxicity tests revealed an improvement in NK cell effector functions leading to increased tumor cell recognition and killing, while we did not observe any direct effect of IL15 on growth and viability of MM cells.

Integration of IL15 in the immunotherapeutic arsenal is limited by the unfavorable pharmacokinetic properties. Therefore, for clinical application and to restore both innate and adaptive immunity, we evaluated impact of NKTR-255, a polymer-conjugated IL15 receptor agonist designed to engage the IL-15 pathway to stimulate and expand natural killer (NK) cells and promote the survival and expansion of central memory CD8+ T cells without inducing suppressive regulatory T cells. Treatment with NKTR-255 enhanced the number and function of both NK and CD8+ effector memory T cell populations in PBMC from HD and MM patients in a dose dependent manner. Interestingly, the natural killer T (NKT) cells, heterogeneous group of T cells that share properties of both T cells and NK cells with important role in MM, were also increased in number by NKTR-255. To evaluate if NKTR-255 increases NK recognition of MM cells, cytotoxicity tests were performed using several MM cell lines and primary MM cells as targets, and both NK cells purified from PBMC of HD and MM patients as effectors. NKTR-255 was able to revert the inhibitory status of NK cells from MM patients (via induction of NKG2D expression), and significantly increase NK susceptibility of the MM cells in a dose dependent manner.

Taken together, our data suggest a significant impact of NKTR-255 on the activation of effector cell function to efficiently target MM cells. This study has important translational implications and highlights the importance of restoring the balance between innate and adaptive immunity in MM.