Daratumumab enhances NK cell cytotoxicity

Natural killer (NK) cells have an intrinsic ability to kill tumor cells without any priming. Importantly, they are selective in their targeting and spare non-cancerous cells, making NK cell-based immunotherapy a desirable therapeutic approach. However, the tumor microenvironment (TME) impedes the anti-tumor effects of NK cells due to the presence of several TME factors (TMEFs), which also contribute to the accumulation of therapy-resistant cells. Therefore, in order for adoptive NK therapeutic strategies to succeed, the suppressive TME needs to be overcome, and this can be done by either enhancing the activating signals or dampening any inhibitory input. One of the activating signals is CD16 engagement by the antibody Fc region and subsequent antibody dependent cell-mediated cytotoxicity (ADCC). Since daratumumab (dara) is a clinically defined antibody targeting CD38 on Multiple Myeloma (MM) cells, this could be utilized not only to target MM cells directly but also to activate NK-cells via ADCC. Minimizing signaling via killer immunoglobulin-like receptors (KIRs) is another approach to enhance NK cell activity; KIR-ligand mismatched NK cells have been shown to be more potent against MM than KIR-ligand matched receptors.

To further investigate ways to enhance NK cell activation,  Niken M. Mahaweni, from the Division of Hematology, Maastricht University Medical Center, Maastricht, The Netherlands, and colleagues, carried out a series of in-vitro experiments to investigate the efficacy of daratumumab (dara) and KIR-ligand mismatched NK cells in triggering NK cell ADCC activity against MM cells. The results were published in Cancer Immunology, Immunotherapy in March 2018.

Key Findings:

• Inhibition of NK cell cytotoxicity against MM cells by lactate and PGE2:

  • IL-2 activated primary NK cells co-cultured with either MM cell lines or controls

  • Hypoxia and lactate alone did not influence NK cell activity

  • Hypoxia and lactate together led to an average 2.28-fold reduction of NK cell cytotoxicity (P < 0.0001)

  • Hypoxia plus PGE2 was less significant with an average 1.26-fold reduction of NK cell cytotoxicity (P < 0.0001); the possibility this was due to NK cell death was excluded

• Dara triggers ADCC and enhances NK cell cytotoxicity in the presence of TMEFs:

  • Following cytotoxic assays of the tumor cells incubated with or without a number of ADCC-triggering antibodies, dara was selected for further studies

  • Level of CD38 expression remained constant in the presence of TMEF

  • NK cell cytotoxicity increased in CD38-high MM cell lines with addition of dara

  • Dara did not enhance or induce NK cell-mediated ADCC in CD38 negative cell lines

• Induction of NK cell death by dara:

  • Since NK cells also express CD38, cell death of NK cells was examined

  • Dara increased the number of average dead NK cells after 4h of culture (36.66%) in comparison to the absence of daratumumab (21.49%)

  • NK cell death observed with dara after 4h co-culture with the different tumor cell and in the presence of all combinations of TMEF (P < 0.0001)

  • Dara induced NK cell death after only 2h; increased up to 60% after 24h

  • Higher percentage of CD107a+ cells with dara, which indicates that NK cells degranulate in presence of dara

• Enhancement in NK cell anti-MM reactivity in the TME by KIR-ligand mismatched donors

• • Dara increased NK cell degranulation with both KIR-ligand matched NK cells and KIR-ligand mismatched NK cells

  • In absence of dara, degranulation was higher for the KIR-ligand mismatched subset, under all TME conditions, which therefore lowers the activation threshold

This preclinical in-vitro study showed that daratumumab can enhance NK cell-mediated killing of MM cells in the presence of TMEFs (hypoxia, hypoxia/lactate, and hypoxia/PGE2). The observed effect was more specific, as well as more pronounced, in MM cell lines expressing high levels of CD38. An increase in efficacy (degranulation) with the use of KIR-ligand mismatched NK cells against MM target cells, in comparison to matched cells under TMEFs, was also observed. The combination of an ADCC triggering antibody such as daratumumab, and the use of KIR-ligand mismatched donors, therefore provides a suitable platform to induce the NK cell antitumor responses in the presence of TMEFs.