Abstract
Purpose: :
To determine mechanisms which inhibit growth of immunogenic tumors transplanted in the anterior chamber (a.c.) of the eye of splenectomized mice.
Methods: :
E.G7-OVA, a murine tumor cell line that expresses chicken ovalbumin (OVA) as a surrogate tumor antigen was transduced to express fire fly luciferase by lentiviral infection. Wild type C57Bl/6 (B6), B6 mice depleted of CD8+ T cells by antibody administration, and immunodeficient B6 strains (NOS-2-/-, GP91phox-/-) were splenectomized, received a sham surgery, or were untreated prior to E.G7-OVAluciferase injection in the a.c. Ocular tumor growth was then monitored by bioluminescent imaging using an IVIS® instrument (Caliper Life Sciences, Hopkinton, MA) or by flow cytometric enumeration of tumors in collagenase digested eyes. In some experiments, naïve OVA-specific CD8+ OT-I T cells were given intravenously prior to ocular tumor injection.
Results: :
All B6 mice injected with 103 or 104 E.G7-OVAluciferase cells in the a.c. developed progressively growing ocular tumors associated with increasing bioluminescence intensity within the eye over time. In contrast, ocular tumors regressed and bioluminescence decreased in splenectomized mice. Ocular tumor regression was comparable in splenectomized NOS-2-/-, and GP91phox-/- mice whereas regression was reduced or completely abrogated in splenectomized mice given depleting anti-CD8 antibodies. Tumor-specific CD8+ OT-I T cell expansion in lymph nodes, and infiltration of ocular tumors was equivalent between splenectomized mice and controls. FoxP3+ cells were not observed in ocular tumors.
Conclusions: :
Bioluminescent imaging of transplanted tumors allows for sequential measurements of tumor growth in live animals. E.G7-OVA tumors are rejected by CD8+ T cells in splenectomized mice presumably by direct killing of tumor cells as ocular tumor regression does not require nitric oxide or reactive oxygen production by intratumoral macrophages. Ocular tumor regression was not the result of increased tumor-specific CD8+ T cell expansion, increased tumor infiltration of CD8+ T cells or decreased numbers of intratumoral FoxP3+ Treg.
Keywords: immune tolerance/privilege • immunomodulation/immunoregulation • tumors