Variations in the responses of mouse strains to rat xenografts

The experiment with the congenic resistant strains shows, therefore, that the strain variations that we are studying are not traceable to differences in susceptibility to the overall suppressive action of the ALS that we have employed. Furthermore, in the case of those mouse strains in which unusually long survival of rat skin is observed on immunosuppressed hosts, the survival times of such xenografts exceeds those of allografts. These differences, observed even when allografts and xenografts are applied simultaneously on opposite sides of the same recipients, are often quite large; in some individual cases involving simultaneously placed grafts, the xenograft has survived more than 100 days longer than the allograft. This finding, together with the observation that primarily vascularized xenografts behave as do free grafts of skin, raises the possibility that in some patients xenografts may provide more effective therapy than allografts would. Apart from this practical consideration, the phenomena described here warrant further investigation in so far as they suggest differences between responses to xenografts and responses to allografts.