Complex sentence: HLA gene products (antigen-presenting, cell-surface receptors) did not evolve to be transplantation antigens or to interfere with transplantation, organ transplantation was not a selective factor until 1960, certain HLA alleles may be over 200,000 years in age.
Split into simpler sentences: HLA gene products (antigen-presenting, cell-surface receptors) did not evolve to be transplantation antigens or to interfere with transplantation. Organ transplantation was not a selective factor until 1960, certain HLA alleles may be over 200,000 years in age.