Lm. Pilarski et al., RESISTANCE AND SUSCEPTIBILITY TO CYCLOSPORINE-A AS CD3(-)4(-)8(-) HUMAN THYMOCYTES DIFFERENTIATE IN-VITRO, Scandinavian journal of immunology, 39(4), 1994, pp. 363-372
Human T-cell development appears to be relatively resistant to cyclosp
orin A (CsA). Children exposed to CsA in utero as part of kidney trans
plant maintenance have few abnormalities. The objective of the study d
escribed here was to analyse the effects of CsA on the development in
vitro of human multinegative (MN) (CD3(-)4(-)8(-)) thymocytes as a mod
el system for thymic progenitor development in vivo. MN thymocytes, pr
epared by depletion methods, differentiated in vitro to acquire CD3 an
d undergo transitions in CD45 isoform expression analogous to those po
stulated to occur in vivo. In this work MN thymocytes were cultured wi
th IL-2 and on thymic epithelial cells (TEC) with or without IL-2, eit
her in the presence or absence of CsA. For many thymocyte preparations
, differentiation in the presence of CsA resulted in almost complete i
nhibition of the acquisition of CD3 and of the low Mr isoform CD45R0.
Expression of CD45RA and of total CD45 were reduced but not eliminated
and the density of CD29 was unaffected. For others, neither CD3 nor C
D45 expression was affected, but selective inhibition of TCR delta exp
ression occurred. At all doses of CsA (0.1-100 mu g/ml), MN thymocytes
continued to cycle indicating a CsA-resistant generative compartment.
Treatment of peripheral blood T cells with CsA had no effect on surfa
ce expression of CD3 or CD45 isoforms but did reduce the amount of de
novo-synthesized CD45R0 mRNA. Culture of MN thymocytes on TEC rendered
them virtually resistant to the negative effects of CsA. CD3 acquisit
ion was unhindered and total CD45 remained high, but the transition fr
om CD45RA to CD45R0 appeared to be delayed. In the absence of TEC, exp
ression of both TCR alpha beta and of TCR delta was inhibited, but on
TEC, TCR delta was actually up-regulated in some conditions. The effec
ts of CsA on human thymocyte development appeared to be modulated by t
he physiological state of the donor and the growth conditions to which
the cells were subjected. Conditions which most closely approximated
those manifest in vivo rendered thymocytes most resistant to the negat
ive effects of CsA. The amount of CsA required to affect differentiati
on in vitro was significantly higher than could be attained in vivo su
ggesting that the immunomodulatory effects of CsA in the maintenance o
f organ transplants may derive from an as yet uncharacterized mechanis
m.