Factors contributing to production of virus-free tumors in turkeys by Rous sarcoma virus

Virus-neutralizing factors in tumor extracts and sera, age of the tumor, and the infecting dose of virus are important factors contributing to the infective titer of tumor tissue. Tumors produced with small amounts of virus may contain no demonstrable infective virus, and detectable inhibitory factors may or may not be present in tumor extracts or sera.