CART19 & PCs

[Guest guest]

Re: Re: New Leukemia Treatment Exceeds Expectations

At 03:01 PM 8/17/2011, Al Janski wrote:

>.......research immunologist at the NIAID.

Below are my questions and her answers.

>QUESTION: Can it be assumed that very small amounts of

memory B cells would survive

>ANSWER: Yes, ...... and furthermore many B cells in

effector sites (particularly mucosal sites) do not express

CD19

A related question (on a different CLL listserve) about

" plasma cells " was asked, and my response is below.

Al Janski

------

QUESTION: " .... if you remove a large percentage of CD19+ B

cell what happens to the production of plasma cells? "

I expect most expert immunologists would say they do not

know exactly what would happen, not only to production (with

or without antigen stimulation) of plasma cells (PCs), but

what would happen to those PCs after they are produced, or

what would happen to a variety of other immune regulatory

pathways under different scenarios.

Because all types of Bcells with CD19 are destroyed by

CART19 cells, and because those different Bcells affect so

many different immunological processes, it's difficult to

predict what might happen to production of (antibody-

secreting) PCs or any other immune function, either in the

short-term or long-term for different patients, each with

unique immune system characteristics. Some good things

could result, as in the case of the patient treated with

CART19 cells, described in the recent NEJM paper. However,

on the down-side, as I quoted the NIAID immunologist

" ....massively altering the immune state can cause more harm

than good.... "

A more bottom-line question than whether PCs will be

produced is whether, and how long, will antibodies be

produced by those PCs. To discuss that, more background is

useful.

After exposure to antigen, short-lived, circulating PCs

( " plasmablasts " ) are produced by differentiation (e.g. in

lymph nodes) of memory Bcells, e.g. as an initial defense

against acute infections. Long-lived PCs are produced,

weeks after antigen exposure, from differentiation of

plasmablasts after they migrate to bone marrow. Long-lived

PCs produce the majority of antibodies in blood. Because

these long-lived PCs do not proliferate or migrate from the

marrow, where they produce antibodies, they are now being

considered by some researchers as " memory PCs " . (Reference

#1).

Consequently, if (as the NIAID immunologist expects) some

memory Bcells (with or without CD19) can survive CART19

therapy, plasmablasts could still be produced in response of

memory Bcells exposure to antigens.

However, because plasmablasts (the circulating PCs) express

CD19 (Reference #2), they would be targets for CART19 cells,

and may not survive long enough to produce any short-term

humoral immunity, let alone arriving in the bone marrow to

differentiate into memory PCs.

Unfortunately, because human memory PCs are in such low

levels (relative to other cells) in marrow, there has not

been definitive characterization of these cells.

Previously, it was thought that marrow PCs did not contain

CD19, but more recent studies indicated that CD19 is

" expressed weakly " on marrow PCs (Reference #3)

Even if marrow memory PCs do not express enough CD19 to be

eliminated by CART19, they do not proliferate, and will not

live forever, and, thus, need to be replenished via

differentiation from new plasmablasts (upon exposure of

memory Bcells to antigen).

Because both memory Bcells and PCs decrease with age

(Reference #2), elderly CLL patients start with a lower

baseline of potential for humoral competence.

In summary, it may not be possible to predict whether

humoral (antibodies) memory will survive after CART19

therapy, however, there is reason to believe it might not

survive.

Al Janski

REFERENCES:

1. " Memory B and memory plasma cells " ; T.Yoshida et al.;

Immunological Reviews 2010; Vol. 237: 117 139

ABSTRACT:

http://onlinelibrary.wiley.com/doi/10.1111/j.1600-065X.2010.00938.x/abstract

SNIP....

" The attribute 'memory' to PCs admittedly is unconventional,

but long-lived PCs of bone marrow are resting in terms of

proliferation and migration, and they provide the antibodies

of humoral memory. These antibodies change the reaction of

the immune system to secondary antigenic challenges, by

neutralizing certain amounts of the antigen, i.e. enhancing

the trigger threshold, and by immediately forming antigen-

antibody complexes. These PCs thus fulfill the criteria of

memory cells. "

2. " Circulating human B and plasma cells. Age-associated

changes in counts and detailed characterization of

circulating normal CD138- and CD138+ plasma cells " ; A.

Caraux et al.; Haematologica 2010; Vol. 95:1016-1020

FULL-TEXT: http://www.haematologica.org/cgi/content/full/95/6/1016

INTRODUCTION SNIP.....

" Very low numbers of plasma cells (2/mL) are found in

peripheral blood of healthy donors. Because of their low

count, only few studies have been devoted to characterizing

their phenotype, most of them dealing with newly generated

plasma cells after in vivo immunization. Steady-state

circulating plasma cells lack CD20, express CD19 and

CD38[high]. It has been recently reported that steady-state

circulating plasma cells are mainly of mucosal origin, the

majority of them secreting IgA (84%), expressing CCR10 (56%)

and beta7 integrin (32%). Steady-state circulating plasma

cells are generally termed plasmablasts because only half

express CD138, a proteoglycan that is a hallmark of plasma

cells, while they are CD45+ and HLA-class II+. Plasmablasts

are generated in the lymph nodes, and induced to circulate

for a short period until they will reach a niche in bone

marrow, spleen, mucosa associated lymphoid tissues (MALT) or

lymph nodes. "

3. " An in vitro model of differentiation of memory B cells

into plasmablasts and plasma cells including detailed

phenotypic and molecular characterization " ; M. Jourdan et

al.; Blood. 2009; Vol. 114: 5173-5181

FULL-TEXT: http://bloodjournal.hematologylibrary.org/content/114/25/5173.long

DISCUSSION SNIP......

" An important question is what the differences are between

these in vitro D10 PCs compared with the most studied human

PCs in vivo, that is, tonsil PCs, BMPCs, and peripheral

blood PCs. Tonsil PCs, present in either germinal centers or

follicular and parafollicular zones, express CD20, CD19, HLA

class II, CD45, CD22, CD9, and highly CD38 and do not

express CD62L and CD138. Peripheral blood PCs detected in

healthy persons after tetanus toxoid immunization are CD20-

CD19+ CD45+ CD62L+ HLA class IICD9CD38high and half of them

express CD138. BMPCs express CD138, highly CD38, and CD31,

lack CD20, and 'express weakly' CD19, and half of them

express CD45 and HLA class II. "

[Guest guest]

I suppose a question might be, are the CART19 T cells self-

limiting... meaning do the B-cells return over time, like

they do after Rituxan? Or, once the CART19 is out of the bag

is a major part of the humoral immune system lost and for

how long?

Do CLL patients then become 'The Bubble Boy' as Seinfeld

described it?

~chris

Al Janski wrote:

/message/15844

[Guest guest]

At 11:01 AM 8/25/2011, cllcanada wrote:

>........are the CART19 T cells self-limiting...

>meaning do the B-cells return over time, like

>they do after Rituxan? Or, once the CART19 is

>out of the bag is a major part of the humoral

>immune system lost and for how long?

The " Discussion " in the NEJM paper (by C.H.June & coworkers,

link below) mentioned the recovery of Bcells " within months "

after rituximab treatment of patients with Bcell cancers but

acknowledged " It is not yet clear whether such recovery will

occur in patients whose anti-B-cell T cells persist in

vivo. "

The key difference between an antibody treatment (e.g.

rituximab) and an antibody-producing cell treatment (e.g.

CART19 cells) is the cell treatment can renew itself,

especially if it is being stimulated by antigen. And that

seems to be the case for these CART19 cells, which not only

maintains, but 'increases' itself (1000-fold) above what was

injected.

The Science Translational Medicine paper (by C.H.June &

coworkers, link below) reported that the CART19 Tcells,

originally injected, had differentiated to develop a memory

Tcell phenotype, which persisted until at least 167 days

after injection, apparently as a result of regular

stimulation by CD19 antigen.

This would be consistent with CD19 Bcells continuing to be

produced, but with the CART19 cells both killing those

Bcells before they could accumulate and CART19 cells being

stimulated to persist and proliferate as memory CART19

Tcells. Unless the cycle (of killing and stimulation of the

killer to survive) is interrupted, it seems it will be

difficult for CD19 Bcells to recover.

However, the immune disruption (from the killing of CD19

cells) could have many biochemical facets, which lessens

certainty about what is yet to happen for the patient who is

profiled in these two papers, and whether what has happened

to him is a good predictor for other CLL patients, with

other unique immune features, when they are treated with

CART19 cells.

Although the full-text NEJM paper is no longer freely

available, the Science Translational Medicine paper remains

freely available and contains most of the information in the

NEJM paper.

Al Janski

REFERENCES:

1. " Chimeric Antigen Receptor-Modified T Cells in Chronic

Lymphoid Leukemia " ; D.L.Porter et al.; N Engl J Med 2011;

365:725-733

ABSTRACT: http://www.nejm.org/doi/pdf/10.1056/NEJMoa1103849

DISCUSSION SNIP..........

" Although CD19 is an attractive tumor target, with

expression limited to normal and malignant B cells, there is

concern that persistence of the chimeric antigen receptor T

cells will mediate long-term B-cell deficiency. In fact, in

our patient, B cells were absent from the blood and bone

marrow for at least 6 months after infusion. This patient

did not have recurrent infections. Targeting B cells through

CD20 with rituximab is an effective and relatively safe

strategy for patients with B-cell neoplasms, and long-term

B-cell lymphopenia is manageable. Patients treated with

rituximab have been reported to have a return of B cells

within months after discontinuation of therapy. It is not

yet clear whether such recovery will occur in patients whose

anti-B-cell T cells persist in vivo. "

2. " T Cells with Chimeric Antigen Receptors Have Potent

Antitumor Effects and Can Establish Memory in Patients with

Advanced Leukemia " ; M. Kalos, et al.; Science Translational

Medicine, Vol 3 Issue 95 95ra73, p.1-11.

FULL-TEXT:

http://stm.sciencemag.org/content/3/95/95ra73.full.pdf

RESULTS SNIP.......

" In the CD8+ compartment, at day 56, CART19 CD8+ cells

displayed primarily an effectormemory phenotype (CCR7-,

CD27-, CD28-), consistent with prolonged and robust exposure

to antigen. By day 169, although the phenotype of the CAR-

cell population remained similar to the day 56 cells, the

CART19 population had evolved to contain a population with

features of central memory cells, notably expression of CCR7

and higher levels of CD27 and CD28, as well as cells that

were PD-1-, CD57-, and CD127+. "