No problem. I found the mono p2 paper, it didn't specify the reason for the difference, just there was a difference between the IC90 values at baseline for the responder group and rebound group. The higher density though would explain why the rebound group required more PRO 140 at baseline.

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In addition, no changes in HIV-1 co-receptor tropism following virologic rebound were seen. PhenoSense® Entry results for PRO 140, maraviroc, and AMD3100 showed no significant change in post-treatment IC 50 and IC 90, compared with baseline results in virologic rebound patients. However, there was a noted difference in the IC90 values from virologic rebound (10.8+/−9.28) and non virologic rebound (6.7+/−6. groups on entry analysis indicating that more PRO 140 was required to reach IC90 by the group that was destined to rebound on PRO 140 monotherapy

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However, an aggregate analysis showed that the participants which experienced virologic rebound had higher IC 90 values for PRO 140 at baseline (10.8 μg/mL) compared to participants without virologic rebound (6.7 μg/mL)

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