Cellular immunity to SV40‐induced tumor cells and solubilized tumor‐associated antigens in immune mice using an isotopic footpad assay

Abstract

AbstractThe 125Iodine isotopic footpad (IFP) assay was used to measure cell‐mediated immune (CMI) responses in vivo to intact tumor cells (TC), crude membrane (CM) preparations and NP40 solubilized tumor cell extracts in BALB/c mice immunized to the SV40‐induced tumor mKSA. A correlation was observed between footpad swelling as measured by calipers and the incorporation of 125I‐labelled human serum albumin into footpads of mice challenged with intact tumor cells. The IFP measurements were favored over footpad swelling measurements since the former lack the subjectivity involved in measuring footpad thickness and appear more sensitive and rapid to perform. These studies indicate that tumor‐associated antigens (TAA) on intact TC from SV40‐induced tumors can be recognized in vivo in the IFP assays and the response is specific to the sensitizing tumor in that other syngeneic tumors do not cross‐react. In addition, these data represent the initial success in using solubilized TAA in the IFP assay. Reactivity to TAA on either CM or NP40 crude soluble extracts of mKSA TC were observed, indicating that the required structural integrity for immune recognition of TAA was preserved following cell disruption and solubilization. Thus, NP40 represents a good method of obtaining solubilized TAA from TC membranes. Local adoptive transfer of CMI reactivity to mKSA TC in the IFP assay was achieved with spleen cells, but not serum, from hyperimmune mice, further implicating the cell‐mediated nature of this in vivo response. Finally, the IFP assay appears to be a rapid, reproducible and sensitive method of measuring CMI reactivity to TAA on either intact TC or solubilized from the cell membrane by detergent.