Rous sarcoma recurrence and Rous sarcoma virus growth in chicken muscle

Following Rous sarcoma virus (RSV‐Bryan standard strain) infection and tumor regression in chickens, tumors recurred in 3 of 6 chickens after contralateral inoculation of 10 5 of RSV. In an attempt to understand the mechanism of tumor recurrence, chickens which had recovered from RSV infection were inoculated at the regression site with Rous associated virus (RAV). Tumors recurred in one‐third of those chickens that received three bi‐weekly RAV injections and in one chicken that received only a single RAV injection. The tumors re‐appeared from 6 to 19 weeks after regression of the original tumors and within 4 weeks of the last RAV challenge. RSV was recovered from cultures of a recurring tumor as well as from a wing that developed subcutaneous blistering following RAV inoculations. RSV was also obtained from 40% of “recovered” wing muscles explanted in tissue culture up to 3 months after regression. In addition, RSV was isolated from a tumor that recurred in one of 12 recovered chickens inoculated with Freund's adjuvant. In an attempt to determine if ageing of muscle contributed to resistance to infection and suppression of tumor recurrence, wings of 5‐week‐old and 12‐week‐old chickens were infected with RSV and RAV, or RAV alone. RSV and RAV were recovered from most muscles explanted 48 h or more after RSV infection of 5‐week‐old chickens. However, when muscles from 12‐week‐old chickens were explanted 4 days after infection, very little RSV was recovered, although most of the RAV‐infected wings produced RAV in culture. This suggests that RAV growth in older muscles is probably not the limiting factor in RSV growth. The relationship between various factors involved in resistance to tumor development and tumor recurrence in chickens recovering from RSV infections is discussed.