Re: New Leukemia Treatment Exceeds Expectations

[Guest guest]

At 02:55 AM 8/12/2011, TERJOHA@... wrote:

>we do not know how long the CART19 cells will

>persist since there are no antibodies to

>eliminate them. They will eliminate fresh CD19+

>B cells while they are still active and the

>CD137 moiety might cause them to proliferate indefinitely.

Whenever it is that CART19 cells no longer persist, is there

any risk that some (all?) clones of normal memory B cells

will no longer exist?

Specifically, is it possible for CART19 therapy (or any

other means) to eliminate 100% of memory B cells, such that,

when normal B cells are no longer being eliminated by CART19

cells, a patient will no longer have humoral immunity to

diseases to which that patient has developed immunity over a

life time?

Can it be assumed that very small amounts of memory B cells

would survive in germinal centers despite long-term (10

months or more) presence of CART19 cells? Human memory B

cells have been observed to persist for more than 50 years

(reference below), but, presumably, that persistence is a

result of long-term low-level replication in germinal

centers.

Lymphoid progenitor cells (without CD19) should survive,

but, presumably, those progenitor cells do not contain such

genetic memory.

If memory B cells are completely eliminated, is it possible

for memory T cells to confer specific antigen memory to

naive B cells?

Al Janski

REFERENCE:

" Memory B cells: Effectors of long-lived immune responses "

Eur. J. Immunol. 2009. 39: 2065-2075

http://onlinelibrary.wiley.com/doi/10.1002/eji.200939531/pdf

SNIP.......

Mechanisms underlying the longevity of memory B cells

" ......memory B cells can persist at low but detectable

frequencies for essentially the life of the host (>50 years

in humans) [11, 61, 62]. "

[Guest guest]

All unknown unknowns as Rumsfeld would say

Al Janski wrote:

/message/15741

[Guest guest]

Don't forget the known unknowns... Ya know, I think

Rumsfield had something there when applied to my experience

with the medical powers that be. I have very few actual

dx's, mostly just known unknowns.

C

Dr. Hamblin wrote:

All unknown unknowns as Rumsfeld would say

Al Janski wrote:

/message/15741

[Guest guest]

CD19 marker is apparently lost when B cells mature to become

memory B lymphocytes.

" CD19 is expressed on follicular dendritic cells and B

cells. In fact, it is present on B cells from earliest

recognizable B-lineage cells during development to B-cell

blasts but is lost on maturation to plasma cells. " (long-

lasting cells are called memory B cells.)

Al Janski wrote:

/message/15741

[Guest guest]

:

Memory B-cells are NOT the same as plasma cells,

if my memory serves me right..

Larry

wrote:

> CD19 marker is apparently lost when B cells mature to become

> memory B lymphocytes.

>

> " CD19 is expressed on follicular dendritic cells and B

> cells. In fact, it is present on B cells from earliest

> recognizable B-lineage cells during development to B-cell

> blasts but is lost on maturation to plasma cells. " (long-

> lasting cells are called memory B cells.)

[Guest guest]

At 11:10 AM 8/13/2011, S. wrote:

> CD19 marker is apparently lost when B cells mature to

> become memory B lymphocytes.

Because human antigen-specific memory B cells exist only in

low levels, they have been characterized indirectly by

conversion of memory B cells into antibody-secreting B

cells.

This was the subject of a recent (July14 2011) Blood paper,

which described an approach for direct ex vivo

characterization and isolation of memory B cells. This

paper reported the existence of " decreased " , " intermediate "

levels CD19 on these isolated memory B cells. See link and

SNIPS below.

Whether such intermediate levels of CD19 afford memory B

cells any protection from long-term CART19 therapy is

probably not predictable at this stage.

Al Janski

REFERENCE:

" Ex vivo characterization and isolation of rare memory B

cells with antigen tetramers " ; Blood. 2011;118(2):348-357;

Franz et al.;

http://bloodjournal.hematologylibrary.org/content/118/2/348.abstract

ABSTRACT:

SNIP......

Studying human antigen-specific memory B cells has been

challenging because of low frequencies in peripheral blood,

slow proliferation, and lack of antibody secretion.

Therefore, most studies have relied on conversion of memory

B cells into antibody-secreting cells by in vitro culture.

To facilitate direct ex vivo isolation, we generated

fluorescent antigen tetramers for characterization of memory

B cells by using tetanus toxoid as a model antigen.

RESULTS:

SNIP........

" Consistent with previous studies (Ref.13), we detected an

expanded population of plasmablasts, characterized by high

level expression of CD27 and moderately decreased expression

of CD19 . "

-----

13. Odendahl M, Mei H, Hoyer BF, et al. Generation of

migratory antigen-specific plasma blasts and mobilization of

resident plasma cells in a secondary immune response. Blood.

2005;105(4):1614-1621.

-----

SNIP..........

We first gated on CD19 cells that were negative for a panel

of exclusion markers (CD3, CD14,CD16, 7AAD), then gated on

plasmablasts, identified by high levels of CD27 and an

intermediate level of CD19 expression, and finally on

tetramer CD19 cells.

[Guest guest]

Having previously read Terry's Blog on CART (Chimeric

Antigen Receptor T-cell) technology and 's article on

BiTE (Bispecific T-cell Engager) technology one cannot

helped but be impressed by medical scientists and their

progress in the early stages of Bio-Tinkering to get T-cells

to attack B-cells. When I read of Dr. June's success I was

more alarmed at the voracious nature of the CART-cells than

its efficacy. My cancer/chemo battered kidneys tried to

hide behind my liver when contemplating the TLS (Tumor Lysis

Syndrome) experienced by the patient and described in the

paper. My lay-person take on CART therapy conjured up

another of my animal metaphors as I read of so many members

excitement.

I live in the wilderness with many species of wild and

domestic animals like Coyotes, Fisher Cats, Fox, Bobcats,

Dogs, Cats and yes Bears. Many of these animals help keep a

balance of nature and rarely bother humans but sometimes

bears can become dangerous, culminating in the rare attack

on humans. Let's say a particularly dangerous Bear

population begins to breed like wildfire and the threat to

me becomes a crisis for which my Atlatl and 12 gage shot gun

are no longer able to handle. Along comes a laid off car

salesman offering to sell me a brace of T-Rex dinosaurs that

he guaranties will eat up the nasty Bear clan. Wow! this is

just what I need...... but I don't notice on the contract

that I sign and in fine print of course, that although the

T-Rexes have proven voracious they are pretty dumb due to

small cranial capacity. The guy who trained the T-Rexes to

eat my nasty Bears could not get the beasts to recognize

just the bad Bears of the nasty Bear clan from the good

bears. Training quit at the level where the T-Rexes could

recognize and target all four legged fur bearing animals.

The nasty Bear horde threat, being so urgent, I hastily put

my money down and let the T-Rexes loose. They clean out the

nasty Bears in short order along with the good bears the

fox, coyote, bobcat, fisher, domestic cats, dogs and my

drunk hirsute neighbor who had been crawling up the path to

his cabin one night. Now, losing my garrulous hirsute

neighbor was no big loss I hasten to admit but soon the

environment was overrun by rats and mice who carried the

fleas from which I have now contracted bubonic plague. The

T-Rexes, having eaten all the animals they could recognize

were looking curiously in my direction.

When any new cytotoxic (cell killing) therapy comes on the

scene, look to see if it targets a marker unique to the B-

CANCER cell and not the both the healthy and the cancerous

B-cells. In the case of CART therapy the T-cells go after

CD19 located on all B-cells which will wipe out good guys

even in their youth as well as the bad guys with apparent

rapid efficiency.

The challenge for developing CLL cytotoxic agents, specific

to our cancer cells, is that an idiotype (unique to the

cancer cell) marker on the surface of the B-cancer cells

does not exist or has not been found or cannot yet be

exploited for bio-engineering of T-cells or mAbs (monoclonal

antibodies like Rituximab/Ofatumumab). The inefficiency of

Rituxan/Ofatumumab may prove to be a blessing for those

patients who get a good response and who do not react badly,

like me, in that some of the good guy B cells are left after

therapy and may confer some immune functionality although

too many of the bad guys are also left who evolve to resist

repeated therapy.

Cancer cells are different from non-cancerous healthy cells

for which a functioning immune system can detect and act on.

I will get excited when we have the tools to restore immune

system functionality into eliminating just the cancer cells

or by a technology that can somehow create/recognize a bio-

chemically unique property of the cancer cells that can be

used as an exclusive target for cancer cell extermination.

The current CART technology will might well be highly useful

in the creation and manipulation of a future strategies

based on more knowledge.

KNOW YOUR BEAR! Live in the moment and practice gratitude

for all that we have. Increasing options abound.

WWW

[Guest guest]

Al Janski wrote:

/message/15741

Dr. Terry Hamblin responded:

>All unknown unknowns as Rumsfeld would say

-----------------------------

I asked very similar questions of a friend, who is a bright,

young, research immunologist at the NIAID (National

Institute on Allergies and Infectious Diseases). Below are

my questions, her answers, plus a comment by her.

Al Janski

QUESTION: Is it possible to eliminate 100% of memory B

cells, such that, when normal B cells are no longer being

eliminated, a patient will no longer have humoral immunity

to diseases to which that patient has developed immunity

over a life time?

ANSWER: It is NEVER possible that I've ever seen to

eliminate 100% of any immune cell- even massive chemo

doesn't do this. However anytime you eliminate a memory cell

you will lose humoral immunity to what that cell had memory

too, which is not particularly a good thing.

QUESTION: Can it be assumed that very small amounts of

memory B cells would survive in germinal centers despite

long-term (10 months or more) Tcell-mediated killing of

CD19+ cells?

ANSWER: Yes, this could certainly happen, and even more so

they would remain in effector sites such as GI immune

tissues & lamina propria of GI tract where T cells may not

have easy access, and furthermore many B cells in effector

sites (particularly mucosal sites) do not express CD19 and

it would miss all of them

QUESTION: Are there any lymphoid progenitor cells without

CD19 (which, thus, should survive CD19-targeting) that could

contain such genetic memory? and develop into memory B

cells?

ANSWER: Absolutely- see above

QUESTION: If memory B cells are completely eliminated, is

it possible for memory T cells to confer specific antigen

memory to naive B cells?

ANSWER: B cells & T cells help each other for antigenic

memory, so lack of memory B cells could potentially impede

future priming of naïve B cells. Furthermore, there are T

cell independent pathways of B cell induction and maturation

that could result in priming of B cells without T cell help.

COMMENT: As for the lentiviral vector, it's a new field

that has possibility, but should be viewed very cautiously.

Anytime you introduce a lentivirus there are other

complications that can arise. Also, massively altering the

immune state can cause more harm than good sometimes, and

should be viewed more as a last resort.

[Guest guest]

Friends

So let me see if I have this straight. This is stolen from a

cartoon with a similar dialogue.

Patient:

So doc, with my CLL, I have a clone of lymphocytes that just

keeps proliferating forever, even though they are no longer

filling any helpful role

Doctor:

That's one way to put it.

Patient:

And you want to treat me with a new genetically modified

clone of lymphocytes that seem to keep proliferating forever

even when they are no longer filling any helpful role and

they had been infected with a HIV type virus?

Doctor:

You got it.

Patient.

Are you really a doctor?

Just trying to add some balance to the discussion.

I am really excited about this. See my blog for more details.

http://bkoffman.blogspot.com