Semi-allogeneic vaccine for T-cell lymphoma

Abstract

Background: Experimental results from studies with inbred mice and their syngeneic tumors indicated that the inoculation of semi-allogeneic cell hybrids (derived from the fusion between syngeneic tumor cells and an allogeneic cell line) protects the animal host from a subsequent lethal challenge with unmodified syngeneic tumor cells.

Methods: Semi-allogeneic somatic cell hybrids were generated by the fusion of EL-4 T lymphoma cells (H-2b) and BALB/c-derived renal adenocarcinoma RAG cells (H-2d). Cell hybrids were injected intra-peritoneally (i.p.) in C57BL/6 mice (H-2b) before challenging the mice with a tumorigenic dose of EL-4 cells.

Results: Semi-allogeneic tumor cell hybrids could not form a tumor in the animal host because they expressed allogeneic determinants (H-2d) and were rejected as a transplant. However, they conferred protection against a tumorigenic challenge of EL-4 cells compared to control mice that were mock-vaccinated with i.p.-injected phosphate-buffered saline (PBS) and in which EL-4 lymphomas grew rapidly to a large size in the peritoneal cavity. Screening of spleen-derived RNA by means of focused microarray technology revealed up-regulation of genes involved in the Th-1-type immune response and in the activation of dendritic antigen-presenting cells (APC).

Conclusion: The results of our studies are entirely consistent with the concept that CD80- and CD86-expressing APC play a central role in mediating the immune protection induced by semi-allogeneic vaccines by activating a Th-1 response and instructing T cells responsible for killing autologous tumor cells.

Figure 1

Anti-tumor protection conferred by semi-allogeneic vaccines. The bar graph shows the average tumor weight per mouse and the standard deviation. Differences in tumor weight between mock-vaccinated mice (PBS) and mice vaccinated with semi-allogeneic cell hybrids (Vac) were statistically significant for both challenges: p-values were < 0.0001 and 0.0017 for the 2 × 10⁴ and the 3 × 10⁴ EL-4 lymphoma cells challenge, respectively.

Figure 2

Hematoxylin & Eosin staining of tissue sections from EL-4-derived tumors. Panels A and B show low and high magnification (with scale bars) of a typical EL-4 tumor from a mouse mock-vaccinated with PBS three weeks before challenge. Panels C and D show low and high magnification (with scale bars) of EL-4 tumor sections from a mouse vaccinated with RAG × EL-4 semi-allogeneic hybrids three weeks before challenge. Note, that both tumors appear to be poorly differentiated (anaplastic), and that there are no morphologic features that distinguish them.

Figure 3

Anti-tumor protection conferred by semi-allogeneic vs. allogeneic vaccines. The bar graph shows the average tumor weight per mouse and the standard deviation. Differences in tumor weight between mock-vaccinated mice (Non-Imm) and mice vaccinated with semi-allogeneic cell hybrids (Semi-Allo) were the most significant (p-value < 0.0001). Also significant were differences in tumor weight between mock-vaccinated mice and mice vaccinated with allogeneic RAG cells (p-value = 0.0183), as well as between mice injected with semi-allogeneic vs. allogeneic vaccines (p-value = 0.0458).

Figure 4

Anti-tumor protection conferred by injection of irradiated semi-allogeneic vaccines compared to co-injection of irradiated EL-4 cells plus irradiated RAG cells. The bar graph shows the average tumor weight per mouse and the standard deviation for each group of mice. The five groups were immunized as follows: 1) mock-vaccination (PBS); 2) 1 × 10⁶ irradiated EL-4 cells (iEL-4); 3) 1 × 10⁶ irradiated RAG cells (iRAG); 4) 1 × 10⁶ irradiated EL-4 cells co-injected with 1 × 10⁶ irradiated RAG cells (iEL-4 + iRAG); 5) 1 × 10⁶ irradiated EL-4 × RAG semi-allogeneic somatic cell hybrids (iEL-4 × RAG). Using mock-vaccination (PBS) as a control, the p-values were as follows: iEL-4 p-value = 0.5469; iRAG p-value = 0.3065; iEL-4 + iRAG (co-injection) p-value = 0.0417; and iEL-4 × RAG (hybrids) p-value < 0.00001.