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Sunday, November 09, 2003

HIV ab

I wonder if there is a human antibody which would block HIV infection of CD-4+ cells. It is clear that anti HIV antibodies in infected people do not protect them (they are the first symptom of HIV disease). Killer cells specific for HIV infected cells delay the course of infection, but are usually not enough. Existing vaccines appear to stimulate anti HIV killer cells but not to cause production of blocking antibodies. I can think of two possible explanations. First it is possible that non of the antibodies in the huge human antibody repertoire that bind to the same part of HIV P-130 as host cells do. Second it is possible that HIV particles do not stimulate production of such antibodies as we have. The second case would be much more promising than the first as it has proven possible to make non antigens antigenic by connecting them to haptans (the H. Influenza vaccine works this way).

So I wonder, is there in the human antibody repertoire an antibody which binds to HIV in a way that makes it fall off of CD-4 ? If such an antibody exists it would be useful to identify it. I propose the following experiment

1. bind CD-4 to a solid support
2. add HIV P-130 (or virus particles if you dare work with them)
3. take a library of human igg c-dna in a P-1 expression vector. This is a bacteriophage which displays a protein on its surface. It will also display hybrid proteins. The P-1 system is a well developed way of finding antibodies which bind to a given target.
4. It seems to me that if there is the desired antibody the P-1 which expresses it will bind to HIV-P-130 and make it fall off of the CD-4. Also unrelated to HIV P-1s will just pass through.
5. precipitate the elutant with another anti P-130 antibody.
6. infect e. coli with the precipitant and repeat.

Actually it might be better to add one or two more purification steps.

Addition 1 would be to bind P-130 to a solid support. Run the P-1 library over it. Take the P-1 that stick (can you precipitate with HIV and P-1 expressing antibodies ?). A library of antibody presenting P-1 that stick to HIV would be a fine start.

It is conceivable that a sucrose gradient of the elutant from 4 to isolate particles with mass P-1 particle + 130 or P-1 particle + HIV particle might make sense.

Now would it be possible to go from an antibody to the antigen ? Maybe screaning hybrids of P-130 with good antigens (or interleukins) for binding to the P-1 that knocks HIV off of CD-4 would be a good idea.


An hour or so after writing the above, I have other thoughts. They are about what p-1 expression library to use. One might be c-DNA to igg mRNA from plasma cells of people who have been HIV positive for a long time but have not progressed to AIDs. Here the hope would be that they (or one of them) has not progressed because he or she is producing a blocking antibody. Notice the idea would be to pool from more than one person. One reason a very good very rare antibody might exist is the last stage (post stimulation) of generation of antibody variation via point mutations. Still this would not get the antibodies which might exist but not be produced after infection because of a recognition of self issue related to t-cells (boy that sure is clear e-mail for an explanation).

Another possibility would be not igg cDNA but the fab part of igd (B-cell receptor) heavy chain genes (that is get from the chromosome with some PCR).

Finally if there is a preliminary selection for sticking to HIV some point mutagenesis of the P-1 would get to antibodies that aren’t made by VDJ rearrangement but would appear after activation via the point mutation process mentioned above.

One thing about the pre selectiong for sticking to HIV and/or looking for a rare antibody. It might make sense once one had some clones expressing anti-HIV to subtract them from the library (I’m afraid I would do on nitrocellulose probe with radioactive known clone for the plaques then remove them physically from plates but I am so out of touch). This would make it possible to search for other rarer clones or clones harder to elute or precipitate.

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