A CD4+ T cell infected with human immun­od­e­fi­ciency virus (HIV/​AIDS). Source: http://​www​.pin​na​cle​tox​i​col​ogy​.com

This week’s sci­ence news is a rel­a­tively old story with a new twist: in the jour­nal Blood, sci­en­tists in Ger­many report a pos­si­ble “cure” for infec­tion with the human immun­od­e­fi­ciency virus (HIV), the virus which causes the dis­ease acquired immun­od­e­fi­ciency syn­drome (AIDS).

An Amer­i­can liv­ing in Ger­many became ill with the rare and unfor­tu­nate com­bi­na­tion of AIDS and leukemia. Doc­tors car­ried out a stan­dard, but rad­i­cal and dan­ger­ous, ther­apy to treat the leukemia: they destroyed his native immune sys­tem and replaced it with a new one trans­planted from another patient’s stem cells. As a result, it seems as though the HIV infec­tion has been com­pletely elim­i­nated from the patient’s body.

Now that you’ve sur­vived the jump, here’s some backstory.

The immune sys­tem is extra­or­di­nar­ily com­plex, but to sim­plify, there are two main kinds of cells that mount an immune defense.

The B cells are called “B” because they mature in the chicken’s bursa of Fabri­cius. Luck­ily, in humans, the equiv­a­lent of the bursa also starts with the let­ter B—bone mar­row. These cells are born in the bone mar­row and stay in the bone mar­row to mature. They release a spe­cial kind of pro­tein called an anti­body that binds to invaders. Like Boys, they spit out these anti­bod­ies with­out regard to what hap­pens to them; they just release their anti­bod­ies into the blood­stream on command.

The T cells (called this because they mature in the human thy­mus) are also born in the bone mar­row, travel to the thy­mus to mature, and then travel the body to fight infec­tion using coöper­a­tive meth­ods. The T cells col­lab­o­rate with each other by plot­ting, plan­ning and schem­ing to destroy invaders.

 

This film shows a light-​​hearted treat­ment of how T cells are like the girls in the movie Mean Girls. (If you’re inter­ested in the sub­ject, there is a longer ver­sion with more infor­ma­tion.)
There are sev­eral main types of T cells:

  • T helper (more about these below)
  • T sup­pres­sor (also called T reg­u­la­tor, “peace­maker” T cells), “Amanda Seyfried cells”
  • T cyto­toxic (i.e. “cell killing” T cells), “Lacey Chabert cells”
  • T nat­ural killer cells (Played by Lizzy Caplan. I call these “ninja” cells, because they talk invaders into dying.)

T helper cells direct the immune attack, and are the queen bees or quar­ter­backs of the immune sys­tem. They carry a sur­face pro­tein called CD4, so these are also called “CD4+ cells”. These are the cells that are infected and destroyed by HIV, which ren­ders the immune sys­tem lead­er­less and rudderless.

Leukemias are can­cers of the immune sys­tem which cause uncon­trolled divi­sion in one or more of these immune cells. The stan­dard treat­ment is to kill off the entire immune sys­tem, then find some­one else’s immune sys­tem to start over again. The prob­lem is that the trans­planted immune sys­tem wants to go out and attack every­thing in the recipient’s body, because it’s all for­eign. This is called “graft vs host dis­ease” and this, plus the other pos­si­ble com­pli­ca­tions (e.g. the new immune sys­tem doesn’t “take root”, or an infec­tion kills the patient while their immune sys­tem is inca­pac­i­tated) means that only about half of the patients who undergo this treat­ment survive.

In the present case, the doc­tor who found a com­pat­i­ble immune stem cell donor found a donor whose cells were nat­u­rally resis­tant to HIV. So, the for­mer AIDS patient not only got a new immune sys­tem, but his new immune sys­tem repelled any remain­ing HIV in his blood­stream and tissues.

Cur­rent esti­mates are that 33 mil­lion peo­ple world­wide and well over a mil­lion US cit­i­zens are infected by HIV. The prob­lem is find­ing a com­pat­i­ble donor match and get­ting over the expense (in dol­lars and health) of such a treat­ment. Just for starters, there’s the extended hos­pi­tal­iza­tion under absolutely ster­ile con­di­tions; the lost time and health of the bone mar­row donor; the cost of the “bio­log­ics”, drugs made from liv­ing organ­isms which are more expen­sive than syn­thetic drugs. For exam­ple, treat­ment for child­hood res­pi­ra­tory syn­cy­tial virus (RSV) with the bio­logic palivizumab costs $5,000 per infant treated. Under­stand­ably, many have ques­tioned the cost-​​benefit ratio, but if it were my infant, I’d pay for the treat­ment. The biggest prob­lem with health care is that its pric­ing is what econ­o­mists call inelas­tic.

Let’s say this treat­ment is improved to the point where it rep­re­sents a “cure” for AIDS. An esti­mate of $1 mil­lion treat­ment cost per patient is not out of line. How are we going to cal­cu­late the cost-​​benefit ratio of such a treat­ment? In other words, how do we ration health care?

Each med­ical advance we make forces us closer to a point where we have to make this cal­cu­la­tion. You can call them “death pan­els”, but some­one has to make this deci­sion. Right now, we ration health care based on who can afford to pay the bill, or who can man­age to stiff their insur­ance com­pany with a bill. Is that the fairest, or the best, sys­tem to ration health care?

Because of total inelas­tic­ity, the ques­tion is not whether to ration health care or not. The ques­tion is how that rationing is to be done.

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