Interview by Maggie L. Shaw

Known as a gene therapy pioneer, Zaia has spent almost40 years at City of Hope, in Duarte, California. He was first drawnby the promise of studying cytomegalovirus. Over the decades, hisgroundbreaking research has encompassed HIV/AIDS, cellular gene transfer therapy, immunotherapy, bispecific antibodies, andnow hyperimmune globulin for workers on the frontlines of thecoronavirus disease 2019 (COVID-19) pandemic.

Known as a gene therapy pioneer, Zaia has spent almost40 years at City of Hope, in Duarte, California. He was first drawnby the promise of studying cytomegalovirus. Over the decades, hisgroundbreaking research has encompassed HIV/AIDS, cellular gene transfer therapy, immunotherapy, bispecific antibodies, andnow hyperimmune globulin for workers on the frontlines of thecoronavirus disease 2019 (COVID-19) pandemic. Zaia was recentlyawarded $750,000 from the California Institute for RegenerativeMedicine to study the potential use of convalescent plasmain patients with COVID-19, as well as to create the COVID-19 Coordination Program to aid in this effort.1

Zaia spoke at length about the crucial connections betweenbasic research in HIV/AIDS and developments in gene therapy.This interview has been edited slightly for clarity.

EVIDENCE-BASED ONCOLOGY (EBO): We know that HIV does notelicit a protective immune response in the body. Do you think itis possible to overcome nature in this regard, to trick the immunesystem into fighting HIV to the degree that it can overcome it, suchas interrupting the binding of the virus to the CD4 receptor?

ZAIA: So, lets take that question apart. There is an immuneresponse in the body to HIV, but its just not protective. Thequestion is, why isnt it protective? And could you overcome thatdeficiency? So, one aspect to understand is the ability of the virusto continuously mutate.

If youre familiar with RNA replication, it doesnt have highfidelity, meaning that mistakes occur while copying the newstrand of RNA. Whereas DNA replication has high fidelity, meaningthat once you copy it, its virtually word-for-word precise with onlyan occasional mutation. So, whenever the virus makes 10,000 basepair copies, theres 1 mistake. But the virus is actually only 10,000base pairs long in terms of its RNA. So that means theres about 1naturally occurring mistake in every new virus. And since therecould be billions of new viruses made, there will be literally allthese mutations a day, some of which could help the virus survive.Since the barriers that put up against the virus for continuing itsreplication are limited (eg, immune response, antiviral medications),its not that hard to imagine that a mutation could occurthat gets around a specific barrier When this occurs, it is calledantigen escape or drug resistance.

The deeper understanding of this question is, in the immunerecognition of the virus, the T lymphocytes have a receptor forthe virus called the T-cell receptor; its really an antigen receptorthat can see a specific peptide on the surface of the virus or onthe infected cell. So, the T-cell receptor itself is the problem. Itsexerting this selection, but it is not very flexibleits rigid. Its anall-or-none thing. If the virus can mutate its protein slightly, thenthat peptide never fits into the receptor. Its kind of like a lock andkey. So, we need a T-cell receptor thats more resistant to antigenescape. Could you make an artificial receptor, called a chimericantigen receptor (CAR), that would better resist antigen escape?At City of Hope, weve been trying to make a T-cell receptor thatyou [could] paste on to the T cells genetically so they are better atresisting this inability to detect the mutated part of the virus.Is there a part of the virus that is resistant to mutation? Thereprobably is. The key surface protein is called gp120. And someantibodies are very broadly reactive to all viruses, all HIV viruses.So, a broadly neutralizing antibody can detect multiple different gp120s, all of which are slightly differentbut theres somecommon feature thats recognized by the broadly neutralizingantibodies. If you put that on a T cell, as a chimeric antigenreceptor, the T cell might be more resistant to antigen escape bythe mutating virus.

The other possibility is, what if you use the CD4 receptor? Thatsan almost immutable part of the virus biology, because if thevirus didnt bind to the CD4 receptor, it probably wouldnt be HIV.It would be a different virus, a different lentivirus. But there areCAR T-cell receptors that utilize not the antibody to find the virus,but the CD4 receptor itself to find the virus. In other words, if youput CD4 on the surface of a CD8 cell, it would find all the gp120because the CD4 and gp120 would bind to each other. So that isactually another concept that can be utilized, and thats currentlyin clinical trials at the University of Pennsylvania.2

So, in summary, I think the trick would be to utilize a modificationof a T-cell receptor that would avoid the ability of the virus tomutate around the classical T-cell receptor and allow the immunesystem to see the virus and to control it.

EBO: The holy grail of HIV research for nearly 40 years has beento produce a vaccine. The Thai trial (RV144)3 has been the onlytrial thus far to show that a preventive HIV vaccine is possible.What have been the barriers to reproducing these results? Why hasachieving the goal of developing an AIDS vaccine been so elusive?

ZAIA: Those are good questions. I dont think anyone knows [theanswers] for sure. But 2 factors are probably important. Again,you go back to the virus mutation issue. Its continuous, and now[its] in the presence of immune pressure placed on the virus bythe vaccine. Youll get selection for these mutations. So, I guessthe question is, did the vaccine make an immune response to themost immutable parts of the virus? Probably notvirus mutationis not the only answer to why vaccines fail. It seems to be somethingmore basic than that.

For example, do vaccines induce mucosal immunity? We have amucosal immunity to many viruses that come in contact with ourmucous membranes via nose, throat, etc. Well, HIV would be inthe mucous membranes of the genital tract and rectum, [usually].So, are these vaccines really making a mucosal immunity where its needed? Thats a possible explanation for why the vaccinesare not working.

An area that people just dont understand at the present timeis why you can make a vaccine for certain viruses that wouldnormally come through the respiratory tract and not be able tomake a vaccine for others. Its relevant to COVID. Will we be ableto make an immune response to COVID when we know that theinitial entry point is through the nasal passages? Thatll be themillion-dollar question.

EBO:Can you explain what a lentiviral vector is? Why is it that HIVcan be inactivated outside the body to be used as a safe lentiviralgene therapy, but we cant do the same with the virus internally?

ZAIA: A lentivirus has a certain structure and is made of RNA andprotein. And it fulfills the requirements from some taxonomiccommittee that defines what a lentivirus is. Basically,it is a virus that can do 1 thing very usefully: it canreverse the RNA to DNA, and the DNA can then beintegrated into the host DNA, become part of the host. And that integration is due to an enzyme calledintegrase. So, it has an RNA that also encodes for thisintegrase as well as reverse transcriptase; it turns RNA into DNA. That was a famous discovery at onepoint; it won the Nobel Prize. And so thats whatmakes it a lentivirus.

Now, you can inactivate it in the sense of makingit safe. It has only 9 major proteins, and thoseproteins are important in those elements that Ijust mentioned and in leading to its pathogenicity.You can remove them and still have some of theelements that you need. For example, you couldleave the integrase but remove other things, whichmay make the virus able to replicate and lead toAIDS. But now youd have an incomplete virus thatyou can put a gene into, and it can be delivered to the cell, because the virus can still get into the cell.And it can still have an integrase, which can helpyou integrate that message or that gene into the hostcell. But the virus cant replicate. It has all the otherparts of it that are needed, but replication has beenremoved. You basically neuter the virus by removingcritical genes. Its still allowed to be a good virusfor your useit can get it into the cell, deliver itspayloadbut it just cant replicate.

The question is, why cant we inactivate certainof these critical genes that are important forreplication? And, in fact, you canin vitro. You cancertainly put in inhibitors of all the various proteinsof a virus. Some of those are called small inhibitoryRNAs (siRNA), which are known to block specificallydifferent proteins of a virus and almost any virus.The question is, how do you deliver that siRNA to allcells that are infected? If you have trillions of cellsinfected, how would you get to the last one? Thatsthe issue. So, you can do it in a test tube, but you justcant do it in a human organism.

Now, you might ask, why are you able to getcertain things to work for acute lymphoblasticleukemia but not for HIV?

Well, I think its because the virus can becomelatent and invisible to most systems and theleukemia cannot. The leukemia is robustly growingand expressing all of its proteins and enzymes,and so we [can fight it with] chemicals and otherthings like CAR T cells, and they will destroy thosecells. The HIV is holed up in an inactive form, aso-called reservoir, and that reservoir is the problem.Once its in there, its like a snake in its hole. Youcannot get to it.

EBO: In a 2016 commentary,4 you discuss thefindings by Yang et al that the immune-mobilizingmonoclonal T-cell receptor, or ImmTAV, couldbe an effective new agent against HIV/AIDS dueto its bispecific antibodybindingproperties. It was shown to haveactivity against both p17-expressingactivated and resting CD4 cells. Is theagent proposed by Yang possible andwithout neurotoxicity?

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