NKG2A Expression Is Not per se Detrimental for the Anti-Multiple Myeloma Activity of Activated Natural Killer Cells in an In Vitro System Mimicking the Tumor Microenvironment

Abstract

Natural killer (NK) cell-based immunotherapy is a promising therapy for cancer patients. Inhibitory killer immunoglobulin-like receptors (KIRs) and NKG2A are required for NK cell licensing, but can also inhibit NK cell effector function. Upon reconstitution in a stem cell transplantation setting or after ex vivo NK expansion with IL-2, NKG2A is expressed on a large percentage of NK cells. Since the functional consequences of NKG2A co-expression for activated NK cells are not well known, we compared NKG2A+ vs NKG2A− NK cell subsets in response to K562 cells, multiple myeloma (MM) cell lines and primary MM cells. NK cells were isolated from healthy donors (HLA-C1+C2+Bw4+) and activated overnight with 1,000 U/ml IL-2. NK cell degranulation in subsets expressing KIRs and/or NKG2A was assessed at 21 or 0.6% O2. Activated NKG2A+ NK cell subsets degranulated more vigorously than NKG2A− subsets both at 21 and 0.6% O2. This was irrespective of the presence of KIR and occurred in response to HLA-deficient K562 cells as well as HLA competent, lowly expressing HLA-E MM cell lines. In response to primary MM cells, no inhibitory effects of NKG2A were observed, and NKG2A blockade did not enhance degranulation of NKG2A+ subsets. KIR− NK cells expressing NKG2A degranulated less than their NKG2A− counterparts in response to MM cells having high levels of peptide-induced membrane HLA-E, suggesting that high surface HLA-E levels are required for NKG2A to inhibit activated NK cells. Addition of daratumumab, an anti-CD38 to trigger antibody-dependent cell-mediated cytotoxicity, improved the anti-MM response for all subsets and degranulation of the KIR−NKG2A− “unlicensed” subset was comparable to KIR+ or NKG2A+ licensed subsets. This demonstrates that with potent activation, all subsets can contribute to tumor clearance. Additionally, subsets expressing KIRs mismatched with the HLA ligands on the target cell had the highest level of activation in response to MM cell lines as well as against primary MM. Our current study demonstrated that if NK cells are sufficiently activated, e.g., via cytokine or antibody activation, the (co-)expression of NKG2A receptor may not necessarily be a disadvantage for NK cell-based therapy.

Peripheral Immunotype Correlates with Minimal Residual Disease Status and Is Modulated by Immunomodulatory Drugs in Multiple Myeloma

“…The functional relevance of co-expression of NKG2A on outcome, whether it is beneficial due to enhanced NK cell licensing or detrimental due to inhibitory interactions for anti-MM response, remains to be explored in larger trials. In the context of the laboratory setting, however, NKG2A expression on high-dose IL-2Àactivated NK cells seemed to be more advantageous for the NK cell response, especially against MM cell lines [18]. A better understanding of NK cell biology and its role in disease control is even more important in the context of newer therapeutics (ie, CD38 monoclonal antibodies), which potentially deplete NK cell subsets.…”

HLA Class I Molecules as Immune Checkpoints for NK Cell Alloreactivity and Anti-Viral Immunity in Kidney Transplantation

“…For NKG2C, interaction with HLA-E complexed to an HLA-G derived peptide most potently stimulates NK cells ( 136 , 138 ). Like the inhibitory KIR family members, NKG2A is involved in licensing of NK cells and NKG2A licensed NK cells can mediate more potent responses against HLA-E negative target cells than their non-licensed hyporesponsive counterparts that do not express KIR or NKG2A ( 139 ). Together with the iKIRs, NKG2A is critical in maintaining NK cell tolerance for healthy cells ( 133 ).…”

NK and NKT Cell-Mediated Immune Surveillance against Hematological Malignancies

“…In addition, ex vivo expanded clinical NK cell products harbor a high percentage of NKG2A + NK cells. However, HLA-E expression on primary MM cells is not sufficient to trigger potent inhibitory signaling via CD94 − NKG2A [131]. Creation of missing-self based on interference with NKG2A would potentiate activation of KIR ligand-mismatched NK cells against tumors expressing high levels of HLA-E. KIR ligand interaction using an anti-HLA antibody can be blocked to create missing-self with monoclonal anti-KIR antibody, resulting in enhanced killing of primary MM tumor cells by haploidentical KIR ligand-mismatched NK cells [132].…”