Restoring the Immune System
Dr Fred Valentine
The immune system declines and is destroyed by HIV. The continuous reproduction of virus in the body ends up destroying your immune system. As the virus reproduces itself the CD4 cells die off. The CD4 cells are important to your immune system. But, when you are able to control HIV reproduction, the immune system usually starts to restore itself. Most of the sickness that results from HIV comes from the opportunistic infections that occur because your immune system is low. The ability of the immune system to get back into shape is what keeps you from getting sick.
In Geneva, researchers agreed upon many improvements in the immune system they see after a person starts suppressive antiretroviral therapy: CD4 cell count go up and something that is not talked about much but is also important is that we also see an initial rise in the number of CD8 cells and then they return to normal numbers.
After starting HAART there is a very rapid rise of CD4 cells followed by what is called a second phase rise which is more gradual. If you look at the types of CD4s that are returning, there are two types of CD4s that researchers worry about--the naive cells and the memory cells. The so-called naive cells are not really naive but these are cells that enable your body to respond to new infections they have not seen. It is generally agreed that the rise in CD4 cells is very important in keepng your immune system strong enough to fight off infections.
During HIV infection most people tend to have more memory cells than naive cells because HIV prefers to destroy naive CD4s. Usually, the increases you get in CD4s during the initial rapid phase of increase after starting therapy tends to reflect what you have before starting therapy. So, if you have primarily memory cells that will proportionately increase. If you have less naive cells before therapy you should get an increase in naive CD4 but not as much. Occasionally, you will see a person with a large number of naive cells prior to starting therapy. In that case you will see a nice increase in their number of naive cells.
Commentary from JL-- As stated just above, HIV preferentially destroys naive CD4 cells. As HIV progresses it tends to continue killing off the naive cells. That may be a good reason to start therapy early enough before a person has too much of a decline in naive CD4 cells. It is important preserve these cells. Once you lose them it may be difficult to regain a large number of them. A study reported at the Human Antiretrovirus meeting in Feb '98 said that some individuals with advanced HIV and with low numbers of CD4 cells such as 20 or 40 may have no naive CD4s left. The study results showed such individuals may or may not be able to regain any naive CD4s. Some individuals regained naive CD4s, and some individuals were unable to regain any naive CD4s.
After the initial rise in CD4s we have observed following people for as long as as about 2 years that the rise in CD4 cells can continue through this 2 year period but the rise usually is a slow gradual one. Also good news is that the ratio of naive to memory cells tend to increase over this time period. While we've all been attracted to the dramatic initial rapid rise in CD4 cells, more important is the long sustained rise which accompanies continual viral suppression.
Commentary-- This information is important. In Geneva, it was reported that the amount of improvement in your immune system may be tied to how much viral suppression you get. You probably need profound viral suppression (<50 copies/ml) to realize the best immune system improvement. And, to sustain this improvement in the immune system you must have continual viral suppression. If viral load rises or rebounds the improvement in the immune sytem may decline again. That is why it is important to continue taking your medications with adherence.
We like to think of reconstitution of immune function as restoration in 2 areas: restoring your immune's system ability to respond to infections such as CMV, MAC, candida, PCP, tuberculosis, etc; and, reconsitution of immune responses to HIV itself. It is clearly this early type of reconstitution, that is the development of substantial immune responses to those infections that had been threatening your health that accounts for people not getting sick now. This type of reconstitution has come as a result of potent viral suppression from potent combination therapy.
Lymphocyte Proliferative Responses (LPRs) in HIV Disease
In the next section we are going to talk about lymphocyte proliferative responses, so I'll explain what it means. Proliferation simply means multiplying. It is important to look at the lymphocyte proliferative responses (LPR) of your immune system to the infections we mentioned in the paragraph just above. The LPR reflects the ability of lymphocytes (CD4s are lymphocytes), which are the immunologically important cells, to recognize a foreign bacteria or infection and then respond to it by multiplying. The initial LPR is by CD4 cells which we think enables other types of lymphocytes to also respond such as CD8 cells and NK-cells (natural killer cells). In a person with a normal immune system, the response we're looking for is for the lymphocytes to divide and make more of the same cells that will recognize the foreign bacteria as soon as it enters the body. The foreign bacteria or infection, and HIV can also be called an antigen.
We have known for a while that LPRs to antigens such as candida, MAC, etc. decrease quite early in the disease. In fact, they may decrease proportionately more than the dcrease in CD4 cells. Surprisingly, initially, LPRs to HIV itself do not develop in the vast majority of patients. There are a few individuals in who they develop and we'll discuss them in a minute.
LPRs to HIV antigen requires a process of a series of a number of immunological functions to be mobilized. You have to have a T-cell receptor (TCR) that recognizes that antigen. You need clones of that cell that carry that receptor. You need cells that present the antigen to the receptors on the cells. The lymphocytes have to be triggered simultaneously by stimulating signals such as cytokines. Cytokines are chemicals that signal cells to act. So, we can measure the lymphocyte proliferation response to recognize the presence or absence of an attacked immune system, and to see if there is a good LP response to an antigen.
The LPR is a measure of the memory of the immune system. You don't find a LP response if your immune system has not met that antigen before. If your immune system has seen the specific antigen before, this evidence of immunological memory should be detectable in immunologically normal people.
Long before HIV disease, there was a history that LPRs when present are associated with control of many infections, and are associated with a type of skin test called delayed type hypersensitivity (DTH).
We measure the LP response by taking a sample of a person's lymphocytes in their blood and put them into a testube in the lab along with an antigen. When the lymphocytes see the antigen they divide and multiply.. If you have more cells that respond to that antigen you get a bigger response, and if you have fewer cells responding to that antigen you have less of a response. We measure the level of response by looking at the amount of lymphocyte proliferation that is occurring.
When you suppress virus production you can get a return of the LPR to antigens that were not there previous to starting therapy. If you don't achieve good virus load suppression you tend not to get a good LP response to antigens. He went on to illustrate his point with examples of 3 individuals. One individual got good control of the virus (good suppression of viral load). This person was exposed to the candida antigen and got a good LP response after virus replication was suppressed. Prior to starting therapy when the person had active ongoing viral replication the person did not have this LPR to candida. The second individual did not suppress virus as well following the start of theapy. This person did not get a good LP response to candida antigen.
Important Example. The 3rd individual is interesting and illustrates a concept that is important to understand. This person had less than 100 CD4 count prior to therapy. He had a history of MAC and CMV. After starting therapy with indinavir+AZT+3TC, his virus load was suppressed and his CD4 count increased to well over 400. This person stopped all of his prophylaxis medications for opportunistic infections. Surprisingly, at a CD4 count of 440 he developed a mild case PCP (pneumonia), but one that was confirmed by doing a biopsy. Dr Valentine tested this person's LP response to several antigens (see table below). He had a good LP response to 2 CMV antigens. So, his immune system was responding well to that infection and was indeed keeping it under control. He responded well to a MAC antigen. He responded well to toxo antigens even though he had no history of toxo, but in this geographical area that includes NYC toxo is quite prevalent. So, his immune system was previously exposed to toxo and therefore had mounted a previous response that was stimulated when the toxo antigen was exposed to this person. But, this person did not respond to the PCP antigen. It's as if this person had a gap in the types of antigens their immune system could respond to.
Commentary-- this suggests that the person's immune system may have lost its ability to respond well to PCP. At some point in the course of this person's disease progression, they may have lost their ability to respond to PCP. If HIV therapy were started earlier in the stage of disease of this person, before their CD4 count declined below 100, they may have been able to preserve their LP response to PCP.
These examples suggest that the LP response may in fact reflect a person's ability to control various opportunistic infections.
The following table shows this person's LP response to 2 CMV antigens, a MAC antigen, 2 toxo antigens and the PCP antigen after starting therapy with indinavir+AZT+3TC. The last column shows the LPR of a normal healthy person to those antigens.
LPR After Therapy Started |
LPR of Normal Persons | |
Antigen |
||
| CMV-1 | 66,683 |
90,428 |
| CMV-2 | 48,849 |
96,852 |
| PPD-2 (MAC antigen) | 209,666 |
209,842 |
| Toxo | 72,107 |
112,006 |
| Toxo ST | 77,980 |
107,288 |
| PCP | 364 |
86,874 |
Infections with most viruses are usually controlled with effective immune responses. It is apparent that does not usually occur with HIV. Dr Valentine suggests the goal of full immunological reconstitution ought to include the development of effective immune or LP response to HIV antigens, in addition to effective immune responses to opportunistic pathogens like PCP, MAC, CMV, etc.
New Experimental Approach To Treating HIV Being Researched:
Combining an HIV vaccine (Remune) +HAART
Dr Valentine is now going to show the preliminary results of a study that he presented in Geneva in which he demonstrated that he was able to get a good LP response to HIV in the patients in his study. The follow-up is only out to 20 weeks so we call it preliminary. It is key to follow these individuals for a longer period of time to see if the LP responses translate into actual benefit to the patients. It's too soon to say this therapy aproach is effective.
It's been appreciated for over 10 years that HIV infected individuals develop immune responses to HIV. They develop antibodies to HIV, and that's how we diagnose whether someone has HIV infection. The HIV test looks to see if a person has antibodies to HIV. Infected individuals also develop a cytotoxic T-cell response. But, the LPR is missing in the vast majority of patients. Individuals who have a large LPR to HIV antigens when they walk in the door are few and are called long-term immunological non-progressors (LTNPs). They have very low or undetectable viral loads without having received treatment for HIV. They have a type of immune response that is different than individuals who do progress. There are other types of long-term non-progressors who don't progress for other reasons.
Question-- Is the relationship between these large LP responses to HIV antigens and a good prognosis simply an association, or do large LP responses to HIV antigens and the associated immune responses such as an increased CTL response (cytotoxic T-cell response) cause the control of HIV infection?
For example, it is possible that a LTNP was infected with a wimpy or weak HIV virus. One that was not capable from the beginning of not reproducing very much or very well. This could account both for the reason that this person would have very little virus, very little damage being done to his immune system, and that this non-threatening exposure to HIV early on allowed his immune system to develop this stronger response. Therefore, we don't know if a large LPR actually is the direct cause of a large immune response that controls HIV. Certainly, these LP responses are associated with doing well but we have to conduct additional studies to see if they cause control of HIV infection.
Summarizing so far--
Dr Valentine designed and started a study to see if these LP responses could be stimulated. Individuals received HAART and after about one month when their viral loads were suppressed to undetectable or near undetectable a course of administration of Remune was started. Remune is an HIV vaccine. Research has suggested that following prolonged suppression of viral load with HAART the LPRs to HIV antigens do not appear; although, as Dr Valentine showed above, LPRs to most opportunistic infections do eventually come back.
In the study, after a 4 week course of HAART, individuals were immunized with HIV-1 Immunogen/IFA at weeks 4, 16, and 28. This HIV vaccine is an inactivated virus that was lacking GP120 but contains many viral proteins, and therefore should generate immune responses against a number of different HIV antigens. Individuals were followed for 32 weeks. Today Dr Valentine presents data through week 20 because that is all that has been so far analyzed, although the study is finishing.
Dr Valentine looked at--
Dr Valentine showed slides displaying the LP responses of 3 individuals to the HAART+vaccine treatment; and, he also showed the LP responses of the overall study group to 3 HIV antigens. All 3 individuals had little LP responses to the 3 HIV antigens before immunization, but you can see increasing LP responses to the HIV antigens over the course of the 20 weeks. Dr Valentine described the LP responses for each individual as large. Dr Valentine then showed 3 slides displaying the LP responses of the 7 participants from the NYU site of the study. In each case the aggregate LP responses of the 7 individuals to each of the 3 antigens was large while the study participants receiving HAART without the vaccine did not have a LP response to any of the 3 HIV antigens. Valentine also showed a slide showing that the 7 individuals at the NYU site who received HAART+vaccine had an increase in a chemokine (MIP-1beta) after immunization. Dr Valentine said that he thinks a person can produce LP response to HIV that are normally missing.
Question-- Do the large LPR to HIV antigens induced by a vaccine have the same association with control of HIV as large LPR developed as a consequence of infection as we see with LTNPs?
We don't know the answer to that question and it is a hard question to answer. A large study will soon begin taking a large number of individuals and suppressing their virus with HAART. Half of the individuals will be immunized but not the other half. This study will attempt to answer that question by following all the individuals for a long time to see if there is a difference between the 2 groups in loss of viral suppression. The only other way to get an answer to this critical question is to stop a person's therapy to see if HAART+vaccine therapy controls virus. In fact, several other studies looking at HAART+vaccine will be starting. Participants in one study may be asked to voluntarily stop therapy to see if they have generated from the LPRs enough immunological control of the virus without therapy.
Valentine concluded by saying--we still need to understand where these new CD4s are coming from (the LPR is an increase in CD4 cells specifically targeting HIV antigens), or what's causing this response. This knowledge is important because it might enable us to increase the number and function of CD4 cells by additional means other than suppressing viral load; we need to understand how this immunological response is occurring.
Background. The participants in Valentine's study have chronic infection. This is when HIV ifection has been ongoing for a prolonged period of time. In other words, if a person has had HIV for a number of years, it is considered chronic infection. Immediately following transmission of HIV from one person to another, the person who got newly infected is considered to have acute or primary infection. Dr Bruce Walker has treated a small group of 7 treatment-naive individuals with HAART during this acute infection period. He also examined 4 individuals treated during acute infection with hydroxyurea+ddI+a protease inhibitor. Walker reported all 11 individuals generated strong and increasing CD4 prolierative responses specific to HIV antigens (similar to Valentine's findings), and that these responses were persistent for up to one year of follow-up. Walker also reported that he has not seen a strong CD4 proliferative response without an accompanying strong CTL response (cytotoxic T-cell lymphocytes can attack and kill antigens). Walker says there is an initial CTL response following HIV infection that disappears due to HIV infection. As Dr Valentine stated above the healthy human immune systemmounts a response to invading viruses. But, with HIV something is missing.
A number of researchers say this CTL response is missing or disappears shortly after HIV infection occurs. It is though that HIV destroys this response very quickly. Walker maintains this response may be preserved by starting HAART during acute infection. This notion has been fairly widely recognized and many doctors recommend considering treatment with HAART during acute infection if they can identify that a person has been recently infected. However, opinions are mixed about how long of a window of opportunity one has to treat during this period. Dr Norman Letvin suggests you have a very brief period of time, possibly as short as 1 week. While Walker suggests it may be several months. Studies will try to determine this window of opportunity. Letvin reported results from an animal study at the February '98 Human Retrovirus Conference suggesting that the immune system is stimulated very quickly after infection, and that CTLs are assisting in containing HIV reproduction. He also stated that he and others have thought for a long time that a CTL response is not possible without the CD4 response specific to HIV antigens.
Prior to the Valentine study researchers doubted that you could stimulate a LPR in chronically infected individuals because the response seems to disappear early after infection. As stated above, Valentine's results are preliminary and we must follow individuals treated with this approach to see if real benefits occur. But, these preliminary results are encouraging, and permit us to think that LPRs may be elicited from individuals during chronic infection, and they may prove beneficial.
In the May '98 issue of NATAP Reports, the article on HIV Pathogenesis (p. 35) discusses Bruce Walker's research at more length. It is available on the NATAP web site.
Two recent research developments are relevant to this discussion. At the International Resistance and Streatment Strategies Meeting in Lake Maggiori, Italy just prior to the Genevameeting, Franco Lori reported that 6/12 individuals who had been taking ddI+hydroxyurea from one of their earlier studies had been found to have HIV specific CD4 responses. These are the responses that Bruce Walker reported to have seen in acute infection only when treated with HARRT or in some long-term non-progressors, and the response many doubt could be elicited in chronic infection. This may be the response Valentine thinks he may be seeing in his study of Remune+HAART. Anthony Fauci, of the NIH, reported at a recent meeting at the Institute of Human Virology in September that in a retrospective analysis 3/13 individuals treated with IL-2 and HAART had undetectable virus in the DNA reservoir of memory CD4 cells. The reservoir that Robert Siliciano discovered and reported last year. However, undetectable does not mean there is no virus. They did, however, look at 100 to 600 million cells, but the test is probably imprecise at this level. Further studies are planned. In the ACTG several studies are planned looking at IL-2+HAART+vaccines.