Slide deck used for video presentation to the OCTS conference. Her2-positive CNS metastases plague refractory breast cancer patients. Here we present our wholly novel approach to cell therapy for the treatment of these patients. #celltherapy #oncology #breastcancer

1. A Novel Platform for Cell Therapeutics
Our Journey from Bench to Clinical Development
8 July 2020
Paul D Rennert, President & CSO, Aleta Biotherapeutics

2. CAR T cells work because
they bind tumor antigens
Cytotoxicity: This encounter triggers the CAR
T cell to secrete factors that kill the tumor cells
Serial killing: Each CAR T cell can find and
kill up to 1000 tumor cells
Proliferation: During that time the CAR T cell
reproduces again and again, creating clones
of itself that can carry on the anti-tumor
activity
Persistence: The target tumor protein must
be consistently expressed at a high enough
level to support CAR T cell expansion and
persistence in the patient
OCTS July 7-9, 20202

3. When they work, cell therapies
produce amazing and curative
benefit in relapsed patients with
no other recourse
Approved anti-CD19 CAR T cell
therapies for refractory B cell leukemia
and lymphomas
Emily Whitehead, 8 years after treatment with Kymriah,
with no trace of leukemia, and still carrying her CAR T cells
OCTS July 7-9, 20203

4. OCTS July 7-9, 20204
CAR-T cells that target CD19 have
exemplary characteristics
• CAR-T cell persistence is a natural attribute of anti-CD19 CAR T cells because
they can expand and persist using normal CD19+ B cells
‣ Normal B cells are a non-tumor dependent, self-renewing antigen source
‣ This antigen depot allows the CAR T cells to outlast and outlive the tumor cells
• CAR-T cell fitness is naturally enhanced by the interaction with normal B cells
• anti-CD19 CAR T cells are known to traffic throughout the patient, including
into the central nervous system
Persistence, fitness, trafficking

5. Other CAR T cells just don’t work as well:
why not?
OCTS July 7-9, 20205

6. Critical issues confront CAR T cell
therapeutics for solid tumors
• CAR T Cell Persistence is often poor in solid tumor indications
• CAR T Cell Fitness can be limited by exhaustion and immunosuppression
• CAR T Cell Trafficking may limit access to the tumor
• Antigen Escape thwarts therapy due to the loss of tumor antigen expression
• Patient Safety can be compromised when CAR T cells attack critical normal cells
and tissues
6 OCTS July 7-9, 2020

7. Our technology has two key
elements designed to tackle
these critical issues
OCTS July 7-9, 20207
• The CAR T cell that has exemplary properties, eg. an anti-CD19 CAR T cell
• Bridging Protein technology - CAR-T Engagers link CAR T cells to whatever
antigen(s) we wish to target

8. Bridging proteins as anti-
CD19 CAR T Engagers
OCTS July 7-9, 2020
8
an anti-tumor antigen domain
(eg. with an scFv)
with two anti-tumor antigen domains
(eg. with two different llama VH)
with an anti-tumor antigen VH
and an anti-albumin VH
• single antigen
• dual antigen
• half-life extended
PromoterCAR192Adualepitopebridgingprotein
CAR19
omoterCAR192Adualepitopebridgingprotein
CAR19
CD19 VH-1 VH-2
CAR19
CD19
PromoterCAR192Adualepitopebridgingprotein
CAR19CD19
CAR19 2A dual epitope bridging protein
VH-1 VH-2
Vh
Vl

9. Delivery of bridging proteins
OCTS July 7-9, 2020
9
• Biologic delivery by injection
• Lentiviral delivery from a CAR T cell
• Oncolytic viral delivery from a targeted tumor cell

10. Bridging protein characteristics:
- simple, modular, multi-antigen, adaptable
OCTS July 7-9, 2020
10
Anti-CD19 CAR T cell characteristics:
- persistence, fitness, trafficking

11. Putting the pieces together …
OCTS July 7-9, 2020
11

12. Bridging proteins coat any
tumor cell with CD19
• The bridging protein is the CD19 extracellular domain linked to antibody
domains that bind to tumor antigens, thus coating the tumor with CD19.
the antibody fragment
binds a tumor antigen
12 OCTS July 7-9, 2020
PromoterCAR192Adualepitopebridgingprotein
CAR19CD19
CAR19
Tumor
Celltumor
antigen
binding
CD19
CAR19
PromoterCAR192Adualepitopebridgingprotein
CAR19CD19
target antigens
Any tumor cell can be coated with CD19

13. Bridging proteins direct anti-CD19 CAR T
cells to attack any tumor cell
anti-tumor protein
13 OCTS July 7-9, 2020
PromoterCAR192Adualepitopebridgingprotein
CAR19CD19
CAR19
Tumor
Celltumor
antigen
binding
CD19
CAR19
PromoterCAR192Adualepitopebridgingprotein
CAR19CD19
anti-CD19 CAR T cell
add CAR T cells
tumor cells are killedCAR T cell sees CD19

14. Promoter CAR19 2A dual epitope bridging protein
CAR19
CD19-anti-tumor antigen
• How best to deliver the bridging protein so that it can get to the tumor?
• Viral expression allows the CAR T cells to secrete the bridging protein, eg. lentiviral expression
from a T cell: “all-in-one delivery”
AR192Adualepitopebridgingprotein
CD19
14
The bridging protein sequence is
secreted by anti-CD19 CAR T cell
The CAR is on the T cell surface The bridging protein is secreted from the T cell
OCTS July 7-9, 2020

15. The bridging protein sequence can be encoded into the CAR itself
• Secreted bridging proteins
(blue) coat a solid tumor cell
(red) with CD19
• Now, any CAR-CD19 T cell
that “sees” the CD19 will
kill this solid tumor cell
OCTS July 7-9, 202015
CAR-CD19 T cell
CAR domain (anti-CD19)
• Using a lentiviral vector, we engineer the CAR-CD19 T cell to secrete bridging proteins –
this creates a Trojan Horse: the CAR T cell delivers its own CAR-T engager to attack the
tumor

16. Aleta-002
Treatment of Breast and Lung Cancer
Patients with Her2+ CNS Metastases
Stage: IND Enablement
OCTS July 7-9, 202016
Clinical translation example

17. The bridging protein sequence can be encoded into
the CAR itself
CD19-anti-Her2 BP
triggers potent
cytotoxicity at sub-
nM concentrations
OCTS July 7-9, 202017
CAR-CD19 T cell
CAR domain (anti-CD19)
• Aleta-002 ---- CAR-CD19 T cells that secrete a CD19-anti-Her2
bridging protein
PromoterCAR192Adualepitopebridgingprotein
CAR19CD19
anti-Her2

18. OCTS July 7-9, 2020
Her2-bridging CAR19 T cells secreting a bridging protein
cure solid tumors in vivo
• CAR-CD19 T cells that secrete a CD19-anti-Her2 scFv bridging protein were injected into
mice carrying Her2-positive ovarian carcinoma cells
18
DIED --- treated with control CARs, or untreated
CURED --- treated with CAR-CD19 T cells that
secrete the CD19-anti-Her2 scFv bridging protein

19. These CARs still respond to CD19 –
mice re-challenged with a CD19+ cell (Nalm6)
19
We took 4 of the survivors and re-challenged them,
this time with CD19-positive Nalm6 cells;
as a control we enrolled 3 naive mice:
0 5 10 15 20
0
5×107
1×108
1.5×108
2×108
2.5×108
ALT19-14 Nalm6 challenge
days post Nalm6
Fluxtotal
non-confidential disclosure
cured mice naïve mice
cured mice: no tumor growth
naïve mice: lethal leukemia

20. non-confidential disclosure
Re-stimulation of Her2-bridging CAR-CD19 T cells
20
• Serial re-stimulation assays evaluate
cytotoxicity and proliferation
• Re-stimulation by a B cell line, but not
a solid tumor cell line, profoundly
induced robust CAR T cell proliferation
• Remaining cells in each case are
cytotoxic – the extent of proliferation is
different
• This remarkable result may further
explain the poor expansion and
persistence properties of CAR T cell
directed to solid tumor antigens
SKOV3 restimulation RAJI restimulation
CAR-only CAR+SKOV3 CAR-only CAR+RAJI
day 4, 1 stimulation
day 8, 2 stimulations
day 12, 3 stimulations
day 15, 4 stimulations

21. This cell therapy is uniquely and specifically
designed to treat Her2-positive CNS metastases
– a huge clinical need
• 270,000 newly diagnosed breast cancer patients/US/year, 20% are Her2-positive
• 230,000 newly diagnosed lung cancer patients/US/year, ~5% are Her2-positive
 230,000 newly diagnosed colorectal cancer patients/US/year, ~4% are Her2-positive
Relapsing Her2-positive cancer patients commonly have CNS metastases
Relapsing patients with CNS metastases have a poor prognosis and limited
therapeutic options – antibody therapy does not treat CNS disease
OCTS July 7-9, 202021

22. Using Her2-bridging CAR-CD19 T cells
to treat CNS metastases
• The CAR T cells will expand in the periphery due to the
provision of CD19+ normal B cells
• Activated CAR T cells will productively traffic into the
CNS
‣ CNS-resident B cell leukemias and lymphomas are
cleared in patients successfully treated with CAR-
CD19 cellular therapy
• CAR T cells that exit the CNS will encounter B cells again
in the periphery
22 OCTS July 7-9, 2020

23. • This is an indication where our technology provides a unique advantage – activation and
persistence provided systemically (CD19-positive B cells) and locally - at the site of Her2-
positive metastasis in the CNS.
• Patients remain on standard of care therapy to control systemic disease = they do not
have to stop trastuzumab/pertuzumab treatment.
• These therapeutic profile is wholly unique and cannot be achieved by CARs directed to
Her2 or by any biologic therapies.
Aleta-002: Program value and differentiation
OCTS July 7-9, 202023

24. Aleta-003
Treatment of CNS Cancers with
multi-antigen targeting CAR T
therapy
Stage: preclinical
24 OCTS July 7-9, 2020
Program extension

25. Examples Patients Antigens Expressed
Glioblastoma / astrocytoma • pediatric and adult Her2, B7H3, IL13Ra2
Medulloblastoma
• rare pediatric cancer
• very rare in adults
Her2, B7H3, B7H6
Ependymoma
• rare pediatric cancer
• very rare in adults
Her2, B7H3, B7H6
Meningioma • pediatric and adult Her2, B7H3, IL13Ra2
Antigen selection for refractory CNS tumors
• How can we create a therapeutic to treat diverse CNS cancers?
• We focused on the pattern of tumor protein expression, and then designed bispecific bridging
proteins that Her2, B7H3 and other tumor antigens
25

26. CAR-CD19-mediated cytotoxicity
by single and dual-antigen
bridging proteins
26
single
dual
single IC50 = 100pM = 6 ngs/ml
dual IC50 = 2.5 pM = 200 pgs/ml
• single antigen and dual antigen
targeting of a breast cancer cell line
• dual antigen targeting shifts potency
dramatically
• antigen expression patterns suggest
safe targeting combinations
• local delivery is possible (eg. AdV)

27. OCTS July 7-9, 2020
Aleta’s Pipeline: diverse programs
moving into development
27
Dual-Antigen

28. Thank you
OCTS July 7-9, 2020