CLL HSCs; CART19; SPs

[Guest guest]

Re: CLL HSCs - implications?

At 01:38 PM 9/12/2011, Al Janski wrote:

> " CLL and leukemic stem cells " (Dr.Hamblin blog, Sept12)

>http://mutated-unmuated.blogspot.com/2011/09/cll-and-leukemic-stem-cells.html

SNIP........Dr. Hamblin wrote: " The concept if that there is

a damaged hemopoietic stem cell (HSC) that feeds in to the

tumor that does not carry the same markers as the tumor and

would therefore not be susceptible to the type of treatment

that would be effective for the bulk of the tumor cells. "

One of the implications of Dr. Hamblin's insight (that CLL

HSCs would not be susceptible to effective treatments for

mature CLL cells) is that it also applies to the recently

published CART19 Tcell immunotherapy (by June & coworkers;

in Porter et al. & Kalos, et al.; links below).

If indeed CLL HSCs are the predecessor cells to mature CLL

cells, then targeting CD19 with CART19 Tcells would not be

expected to eliminate CLL, because CLL HSCs are negative for

CD19 (Kikushige et al., link below).

However, CART19 therapy may still be effective in keeping

the disease under control, by eliminating the predecessor

CLL cells (e.g. pro-Bcells), which would evolve from CLL

HSCs but are positive for CD19. As such, for prolonged

benefit, it would be necessary for memory CART19 Tcells to

endure and remain competent to be activated by CD19 protein

antigen.

Interestingly, CD19 positive " stem-like " CLL cells have been

isolated (by Gross et al. 2010, and others). These " side-

population " (SP) CLL cells were chemoresistant to

fludarabine, and existed innately in patients, as well as

being increased ( " acquired " ) after fludarabine treatment.

These SP CLL cells may be derived from maturation of CLL

HSCs and may be predecessors to some of the mature CLL cell

population, which might then be more chemoresistant than

other CLL cells derived from other precursor cells.

Further, isolated CLL SP cells have been used for

vaccination in patients ( et al., 2010), eliciting a

cytotoxic Tcell response that was specific for CLL SP cells,

rather than for mature CLL cells. However, the anti-SP CLL

T-cell response was lost 4-6 weeks after vaccine

administration ceased. Apparently, a good memory Tcell

response, like that observed in the CART19 study, did not

exist for this anti-SP response.

What is interesting is that et al. could not detect

any unique 'surface' antigen on SP CLL cells that was not

present on the larger population of CLL cells. And it is

noteworthy that the process by which the stem-like SP CLL

cells are isolated involves first selecting for cells

containing proteins (i.e. " ABC transporter proteins " ) that

are 'not' on the cell surface, but are 'intracellular'

proteins that are known to serve to pump out

chemotherapeutic agents (e.g. fludarabine) from a variety of

cancer cells, thus making them chemoresistant. Before

vaccination of patients, this knowledge was used to enrich

the SP CLL preparation by killing off residual non-SP CLL

cells with fludarabine.

The possibility exists that the immunogenicity of SP cells

was related to an 'intracellular' protein antigen (e.g. an

ABC transporter protein), despite that notion being contrary

to conventional understanding of cellular antigenicity.

However, that convention may be changing.

Specifically, published last week, a paper (by Guo et al.)

demonstrated anti-tumor activity from either exogenously

administered antibodies or from host-induced antibodies

(i.e. vaccination) against 'intracellular' tumor antigens.

The authors concluded that " This study suggests that

antibody-based therapy and vaccination against cancer may be

extended to a wider variety of intracellular oncoproteins as

therapeutic targets. With cancer treatment becoming more

individualized, the ability to target a whole new list of

intracellular oncoproteins previously thought to be

untargetable by therapeutic antibodies or vaccinations can

expand the scope for tailor-made cancer therapy as well as

usher in a new era of tailor-made cancer vaccines. "

Consequently, maybe it is not necessary that the CART

therapy technology target only surface antigens (like CD19)

on CLL cells, or surface antigens on CLL HSCs, etc. Maybe

better antigen targets can be identified in the

intracellular space of CLL cells, such that benefits (like

not eliminating CD19 normal Bcells) can be achieved.

Al Janski

REFERENCES:

" Self-Renewing Hematopoietic Stem Cell Is the Primary Target

in Pathogenesis of Human Chronic Lymphocytic Leukemia " ; Y.

Kikushige et al.; Cancer Cell 20, 246­259, August 16, 2011

ABSTRACT: http://www.sciencedirect.com/science/article/pii/S1535610811002595

" 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>http://www.nejm.org/doi/pdf/1\

0.1056/NEJMoa1103849

" 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

" B-chronic lymphocytic leukemia chemoresistance involves

innate and acquired leukemic side population cells. " , E.

Gross et al.; Leukemia 24, 1885-1892 (November 2010)

ABSTRACT: http://www.nature.com/leu/journal/v24/n11/full/leu2010176a.html

" Selective elimination of a chemoresistant side population

of B-CLL cells by cytotoxic T lymphocytes in subjects

receiving an autologous hCD40L/IL-2 tumor vaccine " AE

et al.; Leukemia (2010) 24, 563-572 FULL-TEXT:

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2836398/pdf/nihms165734.pdf

" Targeting Intracellular Oncoproteins with Antibody Therapy

or Vaccination " ; Ke Guo et al.; Science Translational

Medicine September 7, 2011 Vol 3 Issue 99 99ra85 ABSTRACT:

http://stm.sciencemag.org/content/3/99/99ra85

PRESS RELEASE: http://www.sciencedaily.com/releases/2011/09/110908104205.htm