On this page of StockholderLetter.com we present the latest annual shareholder letter from Spero Therapeutics, Inc. — ticker symbol SPRO. Reading current and past SPRO letters to shareholders can bring important insights into the investment thesis.

 •  4/28/2025 Letter Continued (Full PDF)
 •  9/1/2023 SPRO Stockholder Letter
 •  4/16/2024 SPRO Stockholder Letter
 •  More "Biotechnology" Category Stockholder Letters
 •  SPRO Benford's Law Stock Score = 71

SPRO Shareholder/Stockholder Letter Transcript:

01234  67238129     4   2   4  
8  8       2   723812   43  18 2    
  7  3832    282  8     9  39  
32 8           8 238     2 4  




012345637346
64809232467154
8 71 48   2662 1
           5 8      
  9   !"
( 71107)94* 93*09607133 64832 1 + 9  #,'  3 464809232464 8 71 4783    + 
  $  &-  . /0& $& ,&,5&.&12&$+     

3 39716232 194* 93*09607133 64832 1 + 9  #,'  3 464809232464 8 71 4783    + 
  $  & $        4&$  ,-$ 15555  5555
8 11      - /& 612&$  !+7 88
6*49#49 .  3 1& -497*4032
86 218 
$&    $      4&. - &,     .  $ &$'
5&/ : $&
 8!    87+
6   & $   &$;6$  , .       . $4 $      $ $    <     
#2 9 6 414/ 0&$
2,&   - .     1  '
#7,,$&   -4$  . 4 /&9&.6  >& -- .& '
#? 48 ,&'
8=      . 6 &   7>& 6&     /  $
8 12$ , &      . 6 &   

9&    $   @  &/&4   & 612&$   ./6,    $& . , ='   !8  
3  /& -& . ./   
6&.6$   & $&    &$&,46$ 6     6&.      #2' -  &7. A
3$ ,   6012 /# '
1 1& -& . &9.    &  :  . $&    &$&,
BCDDCEFGCHIJKLMLLNOPQRPSTUOUQVWPQU
FXYZ
[WU\PV]P^_SC`PSFUSUHGaPQIUG
6&.6$   & $&    &$&,46$ 6     6&.      # ' -  &7. A
1  &
bE]cHPGU`dHWUHIDPQIceGWUQUfcVGQPEGcVPgUSShIECgEVUPVCEU]cVVTUQJPV]UecEU]cEYTSUiLjCeGWUFUHTQcGcUVkHGMlUV3\C(
bE]cHPGU`dHWUHIDPQIceGWUQUfcVGQPEGcVECGQU^TcQU]GCecSUQUOCQGVOTQVTPEGGCFUHGcCENmCQNjn]oCeGWUkHGMlUV3\C(
bE]cHPGU`dHWUHIDPQIgWUGWUQGWUQUfcVGQPEGnNoWPVecSU]PSSQUOCQGVQU^TcQU]GC`UecSU]`dFUHGcCENmCQNjn]oCeGWUFUHTQcGcUVpqHWPEfUkHGCeNrmi]TQcEfGWU
OQUHU]cEfNsDCEGWVnCQeCQVTHWVWCQGUQOUQcC]GWPGGWUQUfcVGQPEGgPVQU^TcQU]GCecSUVTHWQUOCQGVoJPE]nsoWPV`UUEVT`tUHGGCVTHWecScEfQU^TcQUDUEGVeCQGWUOPVGrL
]PdVMlUV(\C3
bE]cHPGU`dHWUHIDPQIgWUGWUQGWUQUfcVGQPEGWPVVT`DcGGU]USUHGQCEcHPSSdURUQdbEGUQPHGcRUuPGPvcSUQU^TcQU]GC`UVT`DcGGU]OTQVTPEGGCYTSUiLjCeYUfTSPGcCEFh[
nwsmsMiLjCeGWcVHWPOGUQo]TQcEfGWUOQUHU]cEfNsDCEGWVnCQeCQVTHWVWCQGUQOUQcC]GWPGGWUQUfcVGQPEGgPVQU^TcQU]GCVT`DcGVTHWecSUVoMlUV(\C3
bE]cHPGU`dHWUHIDPQIgWUGWUQGWUQUfcVGQPEGcVPSPQfUPHHUSUQPGU]ecSUQJPEPHHUSUQPGU]ecSUQJPECEhPHHUSUQPGU]ecSUQJPVDPSSUQQUOCQGcEfHCDOPEdJCQPEUDUQfcEf
fQCgGWHCDOPEdMFUUGWU]UecEcGcCEVCexSPQfUPHHUSUQPGU]ecSUQJyxPHHUSUQPGU]ecSUQJyxVDPSSUQQUOCQGcEfHCDOPEdJyPE]xUDUQfcEffQCgGWHCDOPEdycEYTSUNs`hsCe
GWUpqHWPEfUkHGM
zPQfUPHHUSUQPGU]ecSUQ
kHHUSUQPGU]ecSUQ
3
3
\CEhPHHUSUQPGU]ecSUQ
FDPSSUQQUOCQGcEfHCDOPEd

pDUQfcEffQCgGWHCDOPEd
3
bePEUDUQfcEffQCgGWHCDOPEdJcE]cHPGU`dHWUHIDPQIceGWUQUfcVGQPEGWPVUSUHGU]ECGGCTVUGWUUqGUE]U]GQPEVcGcCEOUQcC]eCQHCDOSdcEfgcGWPEdEUgCQQURcVU]
ecEPEHcPSPHHCTEGcEfVGPE]PQ]VOQCRc]U]OTQVTPEGGCFUHGcCENmnPoCeGWUpqHWPEfUkHGM3
bE]cHPGU`dHWUHIDPQIgWUGWUQGWUQUfcVGQPEGWPVecSU]PQUOCQGCEPE]PGGUVGPGcCEGCcGVDPEPfUDUEG{VPVVUVVDUEGCeGWUUeeUHGcRUEUVVCecGVcEGUQEPSHCEGQCSCRUQ
ecEPEHcPSQUOCQGcEfTE]UQFUHGcCEiLin`oCeGWUFPQ`PEUVhZqSUdkHGnNj|MFMBM}s~sn`oo`dGWUQUfcVGUQU]OT`ScHPHHCTEGcEfecQDGWPGOQUOPQU]CQcVVTU]cGVPT]cGQUOCQGM
3
beVUHTQcGcUVPQUQUfcVGUQU]OTQVTPEGGCFUHGcCENsn`oCeGWUkHGJcE]cHPGU`dHWUHIDPQIgWUGWUQGWUecEPEHcPSVGPGUDUEGVCeGWUQUfcVGQPEGcEHST]U]cEGWUecScEfQUeSUHGGWU
HCQQUHGcCECePEUQQCQGCOQURcCTVSdcVVTU]ecEPEHcPSVGPGUDUEGVM3
bE]cHPGU`dHWUHIDPQIgWUGWUQPEdCeGWCVUUQQCQHCQQUHGcCEVPQUQUVGPGUDUEGVGWPGQU^TcQU]PQUHCRUQdPEPSdVcVCecEHUEGcRUh`PVU]HCDOUEVPGcCEQUHUcRU]`dPEdCeGWU
QUfcVGQPEG{VUqUHTGcRUCeecHUQV]TQcEfGWUQUSURPEGQUHCRUQdOUQcC]OTQVTPEGGCwsiLMNLuhNn`oM3
bE]cHPGU`dHWUHIDPQIgWUGWUQGWUQUfcVGQPEGcVPVWUSSHCDOPEdnPV]UecEU]cEYTSUNs`hsCeGWUkHGoM lUV3 \C(
[WUPffQUfPGUDPQIUGRPSTUCeHCDDCEVGCHIWUS]`dECEhPeecScPGUVCeGWUQUfcVGQPEGHCDOTGU]`dQUeUQUEHUGCGWUOQcHUCeGWUQUfcVGQPEG{VHCDDCEVGCHIPVCe TEUs  J
sLsiJGWUSPVG`TVcEUVV]PdCeGWUQUfcVGQPEG{VDCVGQUHUEGSdHCDOSUGU]VUHCE]ecVHPS^TPQGUQJgPVPOOQCqcDPGUSdK~rMjDcSScCEn`PVU]CEGWUSPVGQUOCQGU]VPSUOQcHUCE
GWU\PV]P^_SC`PSFUSUHGaPQIUGPVCeVTHW]PGUoMkVCeaPQHWsNJsLsjJGWUQUgUQUjjJrLLJ~iNVWPQUVCeGWUQUfcVGQPEG{VHCDDCEVGCHIJKLMLLNOPQRPSTUOUQVWPQUJ
CTGVGPE]cEfM
5 80 4136218 9* 97345    94 494184
[WUQUfcVGQPEGcEGUE]VGCecSUP]UecEcGcRUOQCqdVGPGUDUEGOTQVTPEGGCYUfTSPGcCENikQUSPGcEfGCGWUsLsjkEETPSaUUGcEfCeFGCHIWCS]UQVgcGWcENsL]PdVCeGWUUE]Ce
GWUQUfcVGQPEG{VecVHPSdUPQUE]U]uUHUD`UQmNJsLsiMXCQGcCEVCeVTHW]UecEcGcRUOQCqdVGPGUDUEGPQUcEHCQOCQPGU]`dQUeUQUEHUcEGCXPQGbbbCeGWcVkEETPSYUOCQGCE
vCQDNLh  GCGWUUqGUEGVGPGU]WUQUcEM


123456786959
  1 
          0                                                                                                                                                                          
         0   ! "#                                                                                                                                                                  
     ,  ,/0 #  ! #0 /                                                                                                                                                              
    1  2#"3 # 0                                                                                                                                                                      
    $  4 5'2#"!  )0 5                                                                                                                                                        
       60  *+  /70 !'"  #                                                                                                                                               
  1  
    .  6 #   +"#  50  #  8 ,"  " 9: 0 /;  '  )* "! <"') #6    #   )     #2 #!<   "+9: 0 /
* ! #0 0                                                                                                                                                                 
    -  6  5     8 70 !   0"   )  '/ 0 "+ 0  !0'," )0 0"   )    '  "+@3 # 0"                                       
    -   B   0  0(   )B '0  0( 70 !'"  #   0"  6 #    0                                                                                      
    =   0  !0'*          )* 33'     #/7                                                                                                             
    A  ,< 5  0   )70 5#       D0 < !!"      "  !!"   0 5  ) 0  !0'70 !'"  #                                     
    A   ,"  #"'   )2#"! ) #                                                                                                                                               
    A   @ < #  +"#   0"                                                                                                                                                        
    A,  70 !'"  #   5#)0 5 "# 05 E #0 )0! 0"   < 2# (      3 ! 0"                                                                          
  1   
     C  70# ! "# ;9F !  0( @++0! #   ),"#3"#  G"( #  !                                                                                           
        9F !  0( ," 3    0"                                                                                                                                              
     1  * ! #0 /@H  # <03"+, # 0     +0!0'@H  #   )6  5      )  '  )* "! <"') #6    #                    
     $  , # 0   ' 0"  <03   )  '  )I#  ! 0"  ; )70# ! "#  ) 3  )  !                                                            
        2#0 !03' !!"   0 5      )* #(0!                                                                                                                       
  1 J
     .  9F<000  ; 0  !0'*       *!< ) '                                                                                                                      
     %   "#  CKL*    #/                                                                                                                                                  
0
25





-A
AC
A 
 1 1 1 1 1=
 1=
 1=
 1=
 1=
 1A



 4/28/2025 Letter Continued (Full PDF)