IL-2 Intratumoral Immunotherapy Enhances CD8+ T Cells That Mediate Destruction of Tumor Cells and Tumor-Associated Vasculature: A Novel Mechanism for IL-2

Abstract

Therapeutic use of IL-2 can generate antitumor immunity; however, a variety of different mechanisms have been reported. We injected IL-2 intratumorally (i.t.) at different stages of growth, using our unique murine model of mesothelioma (AE17; and AE17 transfected with secretory OVA (AE17-sOVA)), and systematically analyzed real-time events as they occurred in vivo. The majority of mice with small tumors when treatment commenced displayed complete tumor regression, remained tumor free for >2 mo, and survived rechallenge with AE17 tumor cells. However, mice with large tumors at the start of treatment failed to respond. Timing experiments showed that IL-2-mediated responses were dependent upon tumor size, not on the duration of disease. Although i.t. IL-2 did not alter tumor Ag presentation in draining lymph nodes, it did enhance a previously primed, endogenous, tumor-specific in vivo CTL response that coincided with regressing tumors. Both CD4+ and CD8+ cells were required for IL-2-mediated tumor eradication, because IL-2 therapy failed in CD4+-depleted, CD8+-depleted, and both CD4+- and CD8+-depleted C57BL/6J animals. Tumor-infiltrating CD8+ T cells, but not CD4+ T cells, increased in association with a marked reduction in tumor-associated vascularity. Destruction of blood vessels required CD8+ T cells, because this did not occur in nude mice or in CD8+-depleted C57BL/6J mice. These results show that repeated doses of i.t. (but not systemic) IL-2 mediates tumor regression via an enhanced endogenous tumor-specific CTL response concomitant with reduced vasculature, thereby demonstrating a novel mechanism for IL-2 activity.

Solid tumors “melt” from the inside after successful CD8 T cell attack

“…Second, IFN-c produced at the tumor site can trigger production of additional inflammatory cytokines and chemokines that subsequently lead to activation and recruitment of NK cells, macrophages or granulocytes [30,31]. Third, IFNc may render tumor stroma that is essential for tumor growth vulnerable to attack by many cells of the immune system [23] and fourth, IFN-c can inhibit tumor angiogenesis [19,20,24,[32][33][34][35].…”

Cytokine-armed vaccinia virus infects the mesothelioma tumor microenvironment to overcome immune tolerance and mediate tumor resolution

“…Injection of AE17 into naı¨ve mice results in mesothelioma tumors histologically similar to human mesothelioma, as described earlier. 35 AE17sOVA was developed by transfecting the AE17 parental cell line with cDNA coding for sOVA, as described earlier. 35 Both cell lines were maintained in media, which consisted of RPMI 1640 (Invitrogen, Auckland, New Zealand) supplemented with 10% turbo bovine serum (Invitrogen), 50 mg ml -1 gentamicin (Pharmacia, Bentley, Australia), 60 mg ml -1 benzylpenicillin (CSL, Melbourne, Australia), and 0.05 mM 2-mercaptoethanol (Merck, West Point, PA).…”

“…35 AE17sOVA was developed by transfecting the AE17 parental cell line with cDNA coding for sOVA, as described earlier. 35 Both cell lines were maintained in media, which consisted of RPMI 1640 (Invitrogen, Auckland, New Zealand) supplemented with 10% turbo bovine serum (Invitrogen), 50 mg ml -1 gentamicin (Pharmacia, Bentley, Australia), 60 mg ml -1 benzylpenicillin (CSL, Melbourne, Australia), and 0.05 mM 2-mercaptoethanol (Merck, West Point, PA). Transfected tumor cell lines were maintained in the same medium supplemented with 400 mg l -1 neomycin analog G418 (geneticin, Invitrogen).…”

“…These data suggest that macrophages may be infected by VV at low levels. 35 or indirectly by increased 'danger' levels and/or local IL-12 concentration that impact on antigen-presenting cells. 36 Thus, we examined splenic cells (as indicators of T cells) exposed to each of the VV constructs.…”

“…32 Thus, in this study we compared VV and FPV viral vectors, both of which express the same marker antigen (hemagglutinin, HA). [24][25][26][27] As both IL-2 and IL-12 have been shown to induce anti-tumor immunity against mesothelioma, [33][34][35][36][37] we compared VV with FPV vectors that encode either IL-2 or IL-12. We show here that i.t.…”