7.42) 
were exposed to virus and vector at 
approximately equal titer and three of 
the four showed transient vector 
expression post transplant. Tests for 
replicating virus in serum, peripheral 
blood mononuclear cells, and bone marrow 
cells, performed two and three years post 
transplant have been negative. PCR 
performed on peripheral blood and bone 
marrow cells for the viral envelope 
region (sensitivity of detection 1 in 
100,000 cells) were negative in all four 
animals. To date no animal has shown any 
clinical illness as a result of virus 
exposure. 
Insertional mutagenesis 
The Moloney murine leukemia virus 
(MoMLV) , the parent retrovirus of LNL-6 , 
can cause neoplasia in mice. Is this a 
threat to patients given marked cells? 
The only human data available are in 
patients receiving TIL marked with LNL-6 
and the data is too early to draw 
significant conclusions. It can be said 
that there has been no apparent toxicity 
or pathology after approximately 60 
patient-months. Evaluating available 
animal data, the chance of primate 
malignancy after RMGT appears to be 
small. Our experience in 21 monkeys 
undergoing a RMGT/autologous bone marrow 
transplantation protocol has shown no 
evidence of neoplasia (mean follow-up of 
2.5 to 4.5 years). There is also no 
published examples of transformation of 
primate cells by a murine retrovirus 
either in vitro or in vivo . Also 
evaluation in TIL populations exposed to 
the LNL-6 vector demonstrate persistence 
of IL-2 dependence in all patients 
tested. 
The factors leading to neoplasia in mice 
are discussed in detail in Appendix 8. 
In brief, the development of leukemia 
after exposure in mice is a complex 
procedure that is likely not directly 
relevant to humans. First, the T-cell 
lymphoma associated with MoMLV is not due 
directly to MoMLV but is caused by a 
Recombinant DNA Research, Volume 15 
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