Activity of liposome-entrapped immunomodulator oligopeptides on human epithelial thymic cells

We have studied the in-vitro effects of liposomal formulations loaded with three oligopeptides (Tp3, Tp4, Tp5), synthetic analogues corresponding to the active site of thymopoietin, on human thymic epithelial cells. The activity of the peptides entrapped in multilamellar vesicles and in stable plurilamellar liposomal vesicles, with or without cholesterol and containing stearylamine or dipalmitoylphosphatidylserine, as positive or negative charge-inducer, was tested. The tetrazolium salt assay was performed as a marker of cell growth. To study the response of thymic epithelial cell cultures to liposome addition-dependent stress, we investigated the changes in the level of heat shock proteins (HSPs70). The results indicated that in-vitro among the peptides tested only Tp4 increased thymic epithelial cell growth. These stimulating effects were improved further when the peptide was entrapped in neutral 1,2-dipalmitoyl-L-α-phosphatidylcholine/cholesterol liposomes. Tp4 was also effective in modulating HSP70 protective effects.