implantation may be due to genomic deletions [12]. However,
Hochedlinger and Jaenisch [16] succeeded in generating
viable offspring from B and T cells but this required an
indirect two-step cloning procedure indicating that terminally
differentiated cells can be reprogrammed to support
full-term development. In previous studies from our laboratory,
using the same HMC system as employed in the
present study, we have obtained blastocyst rate of 24% to
49% with fetal, newborn, and cumulus cells [17], 16% with
somatic cells isolated from milk [18,19], 34% to 51% with
those isolated from seminal plasma [10], and w50% with
urine-and tail skin–derived somatic cells [20]. These results
point to low developmental competence of lymphocytederived
cloned embryos. Because the cleavage rate of
cloned embryos derived from fibroblasts and lymphocytes
was similar in the present study, it can be safely assumed
that the low blastocyst development in lymphocyte derived
NT embryos may not be due to the difficulties encountered
while fusing relatively smaller lymphocytes with the
enucleated oocyte cytoplasts. It could be due to the lower
reprogramming ability of lymphocytes than that of other
donor cell types. Another reason could be the lack of synchronization
of lymphocytes in G0/G1 stage, which has been
reported to be necessary for embryonic development [2]. It
is also possible that the ability of blood-derived lymphocytes
to be reprogrammedmay be lower than that of lymphocytes
obtained from other sources like lymphnodes. After SCNT,
themorula per blastocyst rate ofmouse T cells isolated from
peripheral blood was 12% compared with that of 71% for
natural killer T cells isolated from liver [21].
The cleavage rate and blastocyst rate for lymphocyteand
skin fibroblast–derived cells were not significantly
different among the three individual donors (animals) in
the present study. In our previous study too, we found
similar blastocyst rate for milk- and skin fibroblast–derived
among individual animals [19]. This suggests that the
between-animal variation may not be a major factor
influencing the blastocyst rate. However, Shi et al. [22] reported
the variable blastocyst rate from buffalo fetal fibroblasts
obtained from different donor animals.