Table 1. Comparison of transmission, replication, and pathogenesis of X4-SHIV_SF33A and R5-SHIV_SF162P3.

Route	Virus	Infected/exposed	Peak viremia	Viral set point	SAIDS/infected	Time to SAIDS	Pathology
i.v.	X4-SHIVSF33A	2/2	107	105 to 107	2/2	26 and 40 weeks	Severe loss of peripheral and lymphoid CD4+ T cells, MAI, PCP
	R5-SHIVSF162 P3	2/2	107	102 to 106	1/2	26 weeks	Gradual loss of CD4+ PBMC severe loss of GALT CD4+ T cells, MAI, PCP
IVAG	X4-SHIVSF33A	6/12	105 to 108	103 to 106	6/6	30 weeks to 3 years	Severe loss of peripheral and lymphoid CD4+ T cells, MAI, PCP
	R5-SHIVSF162 P3	7/9	105 to 108	102 to 106	4/7	24-104 weeks	Gradual loss of CD4+ PBMC, severe loss of GALT CD4+ T cells, MAI, PCP

MAI, mycobacterium avum-intracellulare; PCP, pneumocystis carinii pneunomia; PBMC, peripheral blood mononuclear cells; GALT, gut-associated lymphoid tissues. Values for peak viremia and viral set point are RNA copies per ml of plasma.