The previous numbers I've estimated of 50% of new patients and 20% of existing patients appear to hold true for control at viral loads two times lower (better) than antiretroviral therapy (daily pills). Control is not a functional cure. Viral loads at <1500 are considered a functional cure because the risk of transmission is extremely low. However, it does not 100% guarantee an individual is not contagious. This is not guaranteed even at undetectable viral loads. However, under Sangamo's definition of functional cure, perhaps 20% will fall into this category in the 12 patient 1.5g study. The biggest problem is the CD4 counts, while they spike initially they decline over the next 12 months but may barely hold over 500 long term. The next round with 1.5g will have to get CD4 counts up and be able to hold them there otherwise the treatment will not even match ART. This is a serious issue.
There are a couple issues as to whether this method can lead to a functional cure. One is re-treatment, how efficacious will that be on CD4 and VL? We just don't know yet. There is also clearly a cost issue, for why not a double treatment from the start, treating double the number of cells. If you're looking at a cost of goods delivered of $10,000, and a margin of 95%, for a treatment cost of $200,000, then doubling treatment puts the cost greater than the current lifetime cost of ART. Re-treating may be the most cost effective method, but having to go through Cytoxan preconditioning twice instead of once should be considered as part of the equation. In the end this may be a treatment that is two or more times better than current ART treatment.
The future is HSC therapy, which involves a mildly ablative treatment of immune system along the lines of the preconditioning regime for a bone marrow transplant and then transplant of treated stem cells into the bone marrow. In human tissue in mice, it looks like it takes about four weeks for the CCR5-negative progeny to rapidly replace cells depleted by the virus, leading to a polyclonal population that preserves human immune cells at normal levels. Viral loads turn down at six weeks and are eliminated by ten weeks. This rapid response is far more indicative of a cure. This is what we are looking for as being a cure for 80% of new patients and 50% of existing patients, the CCR5 active patients. An IND is expected in 2014.
Under early investigation is the cross-clade work, "Cross-Clade Inhibition of HIV on Primary Cells by CXCR4 or CCR5 Fused To the C34 Peptide From gp41HR2" would bring treatment to an even higher percentage of new and existing patients. I would estimate 95-100%. I haven't been able to find the webcast so can't comment further. No plans for an IND, but this could be a full cure.
Disclosure: I am long SGMO.