ITPK1 Sensitizes Tumor Cells to IgA-dependent Neutrophil Killing In Vivo.

Neutrophils can efficiently trigger cytotoxicity toward tumor cells and other target cells upon engagement of the IgA receptor CD89. However, the cell-intrinsic factors that influence the induction of cell death upon exposure to neutrophil effector mechanisms in vivo remain largely unknown. To uncover genetic regulators that influence target cell sensitivity to IgA-induced neutrophil-mediated killing, we used a human CD89 (hCD89) transgenic mouse model in which IgA-mediated killing of Her2-positive CD47-deficient murine target cells is mediated by neutrophils. Using a genome-wide in vivo screening approach, we demonstrate that deletion of the gene encoding inositol-tetrakisphosphate 1 kinase (ITPK1) increases survival of target cells in anti-Her2 IgA-treated mice. Moreover, we show that this effect depends on neutrophil activity and on the ITPK1 kinase domain. Notably, ITPK1 deficiency did not measurably impact survival of IgA-opsonized target cells in in vitro systems, underscoring the importance of in vivo screening systems to uncover physiologically relevant regulators of neutrophil killing.

The high-affinity IgG receptor, FcgammaRI, plays a central role in antibody therapy of experimental melanoma.

We examined the role of FcgammaR in antibody therapy of metastatic melanoma in wild-type and different FcgammaR knock-out mice. Treatment of B16F10-challenged wild-type mice with TA99 antibody specific for the gp75 tumor antigen resulted in a marked decrease in numbers of lung metastases. Treatment of individual FcgammaR knock-out mice revealed the high-affinity IgG receptor, FcgammaRI (CD64), to represent the central FcgammaR for TA99-induced antitumor effects. The potential of immune-modulating agents to further enhance the protective effect induced by monoclonal antibody (mAb) TA99 was examined in combination treatments consisting of mAb TA99 and a TLR-4 agonist, monophosphoryl lipid A (MPL). MPL did potently boost TA99 antibody-induced effects, and combination therapy was, again, found to be dependent on the presence of FcgammaRI.

CpG-A and B oligodeoxynucleotides enhance the efficacy of antibody therapy by activating different effector cell populations.

Immunostimulatory CpG oligodeoxynucleotides (ODNs) can enhance the therapeutic effect of monoclonal antibodies (mAbs) by enhancing antibody-dependent cell-mediated cytotoxicity (ADCC). Distinct classes of CpG ODNs have been found recently to stimulate different effector cell populations. We used murine cancer models to explore the role of various effector cell populations in the antitumor activity seen with mAbs combined with CpG ODNs of the A and B classes. In the 38C13 syngeneic murine lymphoma model, both CpG A and CpG B enhanced the efficacy of murine antilymphoma mAb. Depletion of natural killer (NK) cells alone markedly decreased the efficacy of therapy with mAbs plus CpG A. In contrast, depletion of both NK cells and granulocytes was required to decrease the efficacy of mAb plus CpG B. A human (h) Fc gamma receptor I (FcgammaRI)-expressing transgenic (Tg) mouse model was used to explore the role of FcgammaRI in therapy with mAb and CpG ODN. CpG B induced up-regulation of FcgammaRI in hFcgammaRI Tg mice, whereas CpG A did not. In vitro CpG B also enhanced ADCC of HER-2/neu-expressing tumor cells by the FcgammaRI-directed bispecific antibody MDX-H210 using hFcgammaRI-positive effector cells. In a solid tumor model, tumor growth was inhibited in Tg mice treated with a combination of MDX-H210 and CpG B. These data suggest that CpG A enhance ADCC largely by activating NK cells. In contrast, other effector cell populations, including granulocytes, contribute to the antitumor activity of CpG B and mAbs. FcgammaRI plays an important role in this activity.

Mac-1 (CD11b/CD18) is crucial for effective Fc receptor-mediated immunity to melanoma.

Antibody-reliant destruction of tumor cells by immune effector cells is mediated by antibody-dependent cellular cytotoxicity, in which Fc receptor (FcR) engagement is crucial. This study documents an important role for the beta(2) integrin Mac-1 (CD11b/CD18) in FcR-mediated protection against melanoma. CD11b-deficient mice, those that lack Mac-1, were less protected by melanoma-specific monoclonal antibody TA99 than wild-type (WT) mice. Significantly more lung metastases and higher tumor loads were observed in Mac-1(-/-) mice. Histologic analyses revealed no differences in neutrophil infiltration of lung tumors between Mac-1(-/-) and WT mice. Importantly, Mac-1(-/-) phagocytes retained the capacity to bind tumor cells, implying that Mac-1 is essential during actual FcR-mediated cytotoxicity. In summary, this study documents Mac-1 to be required for FcR-mediated antimelanoma immunity in vivo and, furthermore, supports a role for neutrophils in melanoma rejection.