Evidence for a post-entry barrier to R5 HIV-1 infection of CD4 memory T cells. by Vyakarnam, A, Eyeson, J, Teo, I, Zuckerman, M, Babaahmady, K, Schuitemaker, H, Shaunak, S, Rostron, T, Rowland-Jones, S, Simmons, G, Clapham, P