ART-Advanced Retroviral

Therapy

            Retroviral therapies were somewhat limited at the beginning of the 21^st century, targeting and interfering with the viral particles, but not combating cells where the virus integrated. A major step in combating retrovirals was the development of so called counter strains, which were the functional component of ART, and which became one of the most important innovations in Human medicine, and was adapted to provide one of the most powerful counter weapons against integrating virii.

            Some types of virus can lead quite complex lifecycles, some types can integrate with the host’s DNA, inserting it’s own genome into the genetic material. The integrated cell can produce viral particles independent of virii, in therapeutic terms the patient will remain infected not after all viral particles are eradicated, but rather when all the cells that can produce viral particles are destroyed. In the early part of the 21^st century a number of pernicious and fatal diseases did not have a ‘cure’ because of the virus’ ability to integrate. It was seen that it was necessary to develop a treatment that could some how discriminate between healthy and integrated cells. One line of investigation lead to the development of counter strains.

            A counter strain can be almost identical to the wild type, but some modification has been made to the genome, the virus would be modified so that it could not integrate into the host cell, but instead that it could recombine with any integrated virus found in the host cell’s genome. Recombination is the process where DNA sequences can base pair together according to their sequence, in effect ‘read’ each other and then pair up with matching sequences. The desired effect was that the modified virus would in effect match up with any integrated viral sequences and then swap out and replace them, in effect replacing the original viral sequence with its own.

Proteins called specific recombinases, which land on matching sequences and then make the cuts and swap the sequences, controlled the mechanism behind this genetic changeover. The problem was that were no specific recombinases that could recognise the ends of the viral genome, so instead human specific recombinases were rapidly evolved in vitro (by in vitro mutagenesis to generate new proteins), and screened by affinity for new recombinases that adhered to the correct viral sequences. Purified proteins were then sequenced and then genetic code produced to create an artificial gene.

The first hope was to produce a non-pathogenic strain, a viral particle that would in effect screen cells for integration, and when viral sequences were found, to recombine and silence them, however lab studies showed that recombination could never be entirely specific in vivo, and that cells which have recombined with the virus could possibly go on to become cancerous, a trait already observed in many viral strains. Instead to avoid the risk of tumour (or lymphoma) the counter viral strain was designed to destroy any cells that it was recombined (or integrated) this removed most of the risk of cancer. The final change in counter viral theory was to actually allow the virus to replicate in the host, before destroying the cells where it could recombine.

The modifications that a therapeutic counter viral would contain not only the recombination function (replacing the integrases), but also be fully capable of replicating, and in addition contain a slow cell suicide trigger (such as a Akt inhibitor), the rather controversial decision to make the virus replicating was eventually permitted because it would allow constant provision of counter virii, which would not only reduce the administration of counter virus, but also regulate its own dosage in the blood stream. In effect the modified virus could only replicate in cells which had already integrated the wild type viral strain, and after recombination and a short period of replication, these cells would then die, and therefore over time the number of integrated cells would decline as the counter virus hunted out and recombined with the infected cells. As production of virus is greatly reduced, and because of some sideline interference effects of the counter strain, the wild strain is progressively reduced, until the counter strain eliminates the wild type virus from the patient. With no integrated cells for the counter virus to use for replication, and the producing cells suiciding, the counter virus tails off with the wild type.