Background: Successful adoptive immunotherapy is hindered by the notable lack of effector lymphocyte entry into tumor sites. Fever-range whole body hyperthermia (WBH) enhances lymphocyte entry into secondary lymphoid organs by increasing the adhesive properties of both lymphocytes and vascular endothelium. Vascular expression of the adhesive molecule ICAM-1 has been demonstrated as a key mediator in promoting improved lymphocyte entry. Accordingly, WBH was explored as an adjunct to overcome limited effector T cell entry into tumors in a model of adoptive immunotherapy.

Methods: Utilizing the mouse melanoma B16/F10 cell line transfected to express the neoantigen ovalbumin (B16-ova), adoptive transfer experiments using ovalbumin specific CD8⁺ T lymphocytes from transgenic mice (OT-1) were performed. Following activation and expansion, OT-1 lymphocytes were transferred intravenously into mice bearing subcutaneous B16-ova tumors. WBH treatment (39.5+0.5°C for 6h) was administered prior to adoptive cell transfer. Characteristics of the tumor vasculature, adoptively transferred cells and tumor growth were evaluated in mice receiving WBH compared to normal thermal (NT) mice.

Results: In mice receiving WBH, B16-ova tumor vasculature demonstrated a marked increase in ICAM-1 expression over NT mice. Unlike the endothelium however, B16-ova cells lacked inducible ICAM-1 expression both in vivo and in vitro. By FACS analyses following expansion, CD8⁺ OT-1 lymphocytes exhibited high levels of adhesion related molecules including CD11a (95%; i.e., the ligand for ICAM-1), CD44 (90%), and CXCR3 (78%). FACS-sorted tumor infiltrating OT-1 cells recovered 24h after adoptive transfer were enriched for CD11a and CXCR3 (99% and 90% respectively). Immunohistochemical studies indicated a ~6 fold increase in homing of OT-1 cells in mice receiving WBH compared to NT controls at both 1h (reflecting early entry) and 24h time points (p<0.001). Mice receiving WBH prior to adoptive transfer further demonstrated a statistically significant reduction in tumor growth compared to NT controls.

Conclusions: Findings that improved clinical outcomes are associated with increased trafficking of tumor-reactive T cells to tumor sites suggest that systemic thermal therapy warrants further study as an adjunct to adoptive immunotherapy in the treatment of cancer. Supported by NIH grants CA79765 and CA094045 and DOD grant W81XWH-04-1-0354.